A pro-Russian rebel helps a couple climb on a damaged bridge across the Siversky Donets river near the village of Stanytsia Luhanska on March 23, 2015. (Photo by Dimitar Dilkoff/AFP Photo)

Ukrainian army soldiers perform a military exercise at a training ground outside Zhitomir, Ukraine, Friday, March 6, 2015. (Photo by Efrem Lukatsky/AP Photo)

Relatives of a worker Dmitri Aleksandrov, killed by a blast at the Zasyadko coal mine, mourn next to his coffin during a funeral ceremony in Donetsk, March 6, 2015. (Photo by Marko Djurica/Reuters)

A grave digger works as his wife watches, at a cemetery where workers killed by a blast at the Zasyadko coal mine will be buried, in Donetsk March 5, 2015. (Photo by Marko Djurica/Reuters)

A Ukrainian serviceman drinks coffee atop an armoured personnel carrier (APC) in Kiev, as he returns from the frontline in eastern Ukraine, March 11, 2015. (Photo by Valentyn Ogirenko/Reuters)

Civilians talk to Ukrainian serviceman who is returning from the front line in eastern Ukraine, in Kiev, March 11, 2015. (Photo by Valentyn Ogirenko/Reuters)

A Ukrainian soldier looks out from an armoured vehicle at a position near Kurakhovo, not far from Donetsk March 11, 2015. (Photo by Gleb Garanich/Reuters)

A dog lies on the ground as members of the Ukrainian armed forces take their positions near Kurakhovo, not far from Donetsk March 11, 2015. (Photo by Gleb Garanich/Reuters)

Members of the Ukrainian armed forces take their positions near Kurakhovo March 11, 2015. (Photo by Gleb Garanich/Reuters)

Refugees, who left their homes because of the fighting in eastern Ukraine, are seen in a volunteer centre in Slaviansk March 12, 2015. (Photo by Gleb Garanich/Reuters)

A pigeon flies from a monument of the Soviet state founder Vladimir Lenin as a Ukrainian flag is seen tied around the monument in the centre of the eastern town of Slaviansk in Donetsk region March 12, 2015. (Photo by Gleb Garanich/Reuters)

A local resident plays with a dog in the eastern town of Slaviansk in Donetsk region March 12, 2015. (Photo by Gleb Garanich/Reuters)

Children play in the centre of the eastern town of Slaviansk in Donetsk region March 12, 2015. (Photo by Gleb Garanich/Reuters)

Children play in the eastern town of Slaviansk in Donetsk region March 12, 2015. (Photo by Gleb Garanich/Reuters)

People queue for free bread distributed by pro-Russian rebels in the village of Chornukhyne near the town of Debaltseve, north-east from Donetsk, March 12, 2015. (Photo by Marko Djurica/Reuters)

People queue for a free food distributed by pro-Russian rebels in the village of Chornukhyne near the town of Debaltseve, north-east from Donetsk, March 12, 2015. (Photo by Marko Djurica/Reuters)

People queue for free food distributed by pro-Russian rebels next to a monument of the Soviet state founder Vladimir Lenin in the village of Chornukhyne near the town of Debaltseve, north-east from Donetsk, March 12, 2015. (Photo by Marko Djurica/Reuters)

A pro-Russian rebel shows his t-shirt depicting Russian President Vladimir Putin at a checkpoint in the village of Chornukhyne near the town of Debaltseve, north-east from Donetsk, March 12, 2015. (Photo by Marko Djurica/Reuters)

A woman walks along a street in the village of Chornukhyne near the town of Debaltseve, north-east from Donetsk, March 12, 2015. (Photo by Marko Djurica/Reuters)

Servicemen load air-to-ground missiles onto a Sukhoi Su-25 jet fighter during a drill at the Russian southern Stavropol region, March 12, 2015. Russia has started military exercises in the country's south, as well as in Georgia's breakaway regions of South Ossetia and Abkhazia and in Crimea, annexed from Ukraine last year, news agency RIA reported on Thursday, citing Russia's Defence Ministry. (Photo by Eduard Korniyenko/Reuters)

A serviceman carries ammunition next to Sukhoi Su-25 jet fighters during a drill at the Russian southern Stavropol region, March 12, 2015. (Photo by Eduard Korniyenko/Reuters)

People queue for free food distributed by pro-Russian rebels in the village of Chornukhyne near the town of Debaltseve, north-east from Donetsk, March 12, 2015. (Photo by Marko Djurica/Reuters)

A woman takes a nap inside a bus while waiting to cross the Uspenka border crossing between Ukraine and Russia, southeast from Donetsk March 15, 2015. (Photo by Marko Djurica/Reuters)

A woman pulls her bags as she is about to cross the Uspenka border crossing between Ukraine and Russia, southeast from Donetsk, March 15, 2015. (Photo by Marko Djurica/Reuters)

A child plays inside a car with his family while waiting to cross the Uspenka border crossing between Ukraine and Russia, southeast from Donetsk, March 15, 2015. (Photo by Marko Djurica/Reuters)

A new volunteer of the Ukrainian interior ministry's special battalion “Sich” takes an oath of allegiance to the country during a ceremony in Kiev March 16, 2015. According to the battalion's commander, the volunteers will be headed to the frontlines in Eastern Ukraine, shortly after their ceremony. (Photo by Valentyn Ogirenko/Reuters)

Women react next to a new volunteer of the Ukrainian interior ministry's special battalion “Sich” during an oath-taking ceremony in Kiev March 16, 2015. (Photo by Valentyn Ogirenko/Reuters)

A relative of a member of the Organization of Ukrainian Nationalists (OUN) reacts before volunteers depart to the frontlines in eastern Ukraine, in central Kiev, March 17, 2015. (Photo by Gleb Garanich/Reuters)

Children present their paintings to servicemen of the Ukrainian national guard battalion "Donbass" before they depart to the frontlines in eastern Ukraine, in central Kiev, March 17, 2015. (Photo by Gleb Garanich/Reuters)

A boy presents his painting to serviceman of the Ukrainian national guard battalion "Donbass" before they depart to the frontlines in eastern Ukraine, in central Kiev, March 17, 2015. (Photo by Gleb Garanich/Reuters)

A member of the People's Militia of Crimea reacts during a ceremony, marking the first anniversary of the Crimean referendum to secede from Ukraine and join Russia, in Simferopol, March 16, 2015. Many members of the current militia joined local pro-Russian self-defence units more than a year ago and were participants of the events, which resulted in Russia's annexation of Ukraine's Black Sea peninsula of Crimea. (Photo by Maxim Shemetov/Reuters)

Valery, 30, a member of the People's Militia of Crimea, shows his son Kirill a medal, which was presented to Valery for merits while serving in a self-defence unit, inside his house on the first anniversary of the Crimean referendum to secede from Ukraine and join Russia, in Simferopol, March 16, 2015. (Photo by Maxim Shemetov/Reuters)

Valery, 30, a member of the People's Militia of Crimea, shows a medal, which was presented to him for merits while serving in a self-defence unit, with his son Kirill saluting in the background, inside their house on the first anniversary of the Crimean referendum to secede from Ukraine and join Russia, in Simferopol March 16, 2015. (Photo by Maxim Shemetov/Reuters)

Valery, 30, a member of the People's Militia of Crimea, talks to his son Kirill inside their house, next to a calendar with a portrait of Russian President Vladimir Putin on the wall, on the first anniversary of the Crimean referendum to secede from Ukraine and join Russia, in Simferopol, March 16, 2015. (Photo by Maxim Shemetov/Reuters)

Members of the People's Militia of Crimea line up before patrolling the territory, during preparations for the first anniversary of the Crimean referendum to secede from Ukraine and join Russia, in Simferopol, March 13, 2015. (Photo by Maxim Shemetov/Reuters)

A Cossack looks on at a festive ceremony marking the first anniversary of the Crimean treaty signing in Sevastopol, March 18, 2015. (Photo by Maxim Shemetov/Reuters)

Members of pro-Russian self-defence units drink alcohol as they take part in celebrations for the first anniversary of the Crimean treaty signing in Sevastopol, March 18, 2015. Russia's flag is flying across Crimea on the anniversary of what President Vladimir Putin calls the region's historic “return home” after Russian troops seized control of it from Ukraine and the people backed annexation in a referendum. (Photo by Maxim Shemetov/Reuters)

People take part in celebrations for the first anniversary of the Crimean treaty signing in Sevastopol, March 18, 2015. (Photo by Maxim Shemetov/Reuters)

A pro-Russian rebel takes cover as a woman from inside a kiosk looks on, during what the rebels said was an anti-terrorist drill in Donetsk, March 18, 2015. (Photo by Marko Djurica/Reuters)

A woman smiles during celebrations for the first anniversary of the Crimean treaty signing in Sevastopol, March 18, 2015. (Photo by Maxim Shemetov/Reuters)

A pro-Russian rebel aims his weapon as people pass by, during what the rebels said was an anti-terrorist drill in Donetsk, March 18, 2015. (Photo by Marko Djurica/Reuters)

Pro-Russian rebels sit inside a truck, during what the rebels said was an anti-terrorist drill in Donetsk, March 18, 2015. (Photo by Marko Djurica/Reuters)

Pro-Russian rebels take their positions on a street, during what the rebels said was an anti-terrorist drill in Donetsk, March 18, 2015. (Photo by Marko Djurica/Reuters)

Pro-Russian rebels take their positions on a street, during what the rebels said was an anti-terrorist drill in Donetsk, March 18, 2015. (Photo by Marko Djurica/Reuters)

Pro-Russian rebels take their positions on a street, during what the rebels said was an anti-terrorist drill in Donetsk, March 18, 2015. (Photo by Marko Djurica/Reuters)

People take part in celebrations for the first anniversary of the Crimean treaty signing in Sevastopol, March 18, 2015. (Photo by Maxim Shemetov/Reuters)

A man holding a Russian flag looks out of the car window during the celebrations for the first anniversary of the Crimean treaty signing in Sevastopol, March 18, 2015. (Photo by Maxim Shemetov/Reuters)

Ukraine's voluntary militia called the Azov Battalion hold artillery training in east Ukraine's village of Urzuf that sits west of the port city of Mariupol on the Azov Sea, March 19, 2015. (Photo by Marko Djurica/Reuters)

Ukraine's voluntary militia called the Azov Battalion holds artillery training in east Ukraine's village of Urzuf that sits west of the port city of Mariupol on the Azov Sea, March 19, 2015. (Photo by Marko Djurica/Reuters)

Ukraine's voluntary militia called the Azov Battalion holds artillery training in east Ukraine's village of Urzuf that sits west of the port city of Mariupol on the Azov Sea, March 19, 2015. (Photo by Marko Djurica/Reuters)

Ukraine's voluntary militia called the Azov Battalion holds artillery training in east Ukraine's village of Urzuf that sits west of the port city of Mariupol on the Azov Sea, March 19, 2015. (Photo by Marko Djurica/Reuters)

Ukraine's voluntary militia called the Azov Battalion holds artillery training in east Ukraine's village of Urzuf that sits west of the port city of Mariupol on the Azov Sea, March 19, 2015. (Photo by Marko Djurica/Reuters)

Ukrainian honour guards carry the coffin bearing the body of Vadym Shalatovsky, a member of Defence Ministry's battalion “Aydar”, who was killed last year in the fighting near Luhansk in eastern Ukraine, during a funeral ceremony at Independence Square in central Kiev March 25, 2015. (Photo by Valentyn Ogirenko/Reuters)

Ukraine's President Petro Poroshenko (L) welcomes a serviceman during a welcome ceremony for first plane from United State with non-lethal aid including ten Humvee vehicles to Ukraine at Borispol airport near Kiev, March 25, 2015. The United States send additional non-lethal aid to Ukraine, including unarmed drones and Humvee vehicles, a U.S. defense official said on March 11. The official, speaking on condition of anonymity, said parts of the U.S. package, including 30 Humvees fortified with additional armor, could come within weeks, while other parts could take longer. The aid comes as Ukraine fights against a Russian-backed rebellion in the east. (Photo by Gleb Garanich/Reuters)

Ukrainian military pilot Nadezhda Savchenko looks out from a defendants' cage as she attends a hearing at the Basmanny district court in Moscow March 26, 2015. Savchenko, 33, was captured by pro-Russian forces and handed over eight months ago to Russia, where she was imprisoned on charges of aiding the killing of two Russian journalists in east Ukraine. At home, she has become a symbol of resistance to Russian aggression. (Photo by Maxim Shemetov/Reuters)

Fighters of the Azov Battalion play chess during a break in the town of Shyrokyne, eastern Ukraine, Sunday, March 22, 2015. (Photo by Mstyslav Chernov/AP Photo)

International Committee of the Red Cross (ICRC) workers prepare bags with bodies of government soldiers to be handed over in Donetsk, eastern Ukraine, Friday, March 27, 2015. Separatists in eastern Ukraine have handed over the bodies of 22 government soldiers killed during the fierce, months-long battle over the airport near the rebel stronghold of Donetsk. The bodies were handed on Friday to a Ukrainian volunteer organization working to recover soldiers killed in a conflict that has claimed more than 6,000 lives. (Photo by Mstyslav Chernov/AP Photo)

A pro-Russian rebel stands in froth of a WWII monument with words reading “Your feat is immortal, eternal glory to you!” near their position at the frontline in a village not far from Luhasnk, eastern Ukraine, Thursday, March 12, 2015. (Photo by Mstyslav Chernov/AP Photo)

In a picture taken on Thursday, February 26, 2015, Tolik Tokar aims an assault rifle, given to him by an Ukrainian serviceman in the village of Chermalyk, eastern Ukraine. A brutal conflict between Russia-backed rebels and Ukrainian government troops has affected more than 1.7 million children on both sides of the front line, according to the UN's children's agency, with some of them sent to orphanages when their parents got killed or went to fight for the rebels, while some parents gave up their foster children because they were no longer receiving benefits for them. (Photo by Evgeniy Maloletka/AP Photo)

In this Thursday, February 26, 2015 file photo a Ukrainian serviceman speaks with a schoolboy in the village of Chermalyk, eastern Ukraine. (Photo by Evgeniy Maloletka/AP Photo)

Recently mobilized Ukrainian soldiers fire an artillery piece during their training session on the shooting range near of Perlyavka village not far of Zhytomyr, Ukraine, 06 March 2015. (Photo by Sergey Dolzhenko/EPA)

Wrecked cars are pictured near a destroyed bridge near Donetsk airport March 3, 2015. (Photo by Baz Ratner/Reuters)