Cars pass a tank position close to the Russian border near the Ukrainian city of Kharkiv March 24, 2014. U.S. President Barack Obama sought support from European allies and China on Monday to isolate Russia over its seizure of Crimea, and Ukraine told its remaining troops to leave the region after Russian forces overran one of Kiev's last bases there. (Photo by Dmitry Neymyrok/Reuters)

A Ukrainian soldier stands guard outside a Ukrainian Army military camp set up on a field close to the Russian border in east Ukraine March 24, 2014. (Photo by Yannis Behrakis/Reuters)

A soldier walks near an armoured personnel carrier in position close to the Russian border near the Ukrainian city of Kharkiv March 24, 2014. (Photo by Dmitry Neymyrok/Reuters)

Ukrainian soldiers are seen atop armoured vehicles at a Ukrainian Army military camp set up on a field close to the Russian border in east Ukraine March 24, 2014. (Photo by Yannis Behrakis/Reuters)

A soldier stands guard near a tank position close to the Russian border near the Ukranian city of Kharkiv March 24, 2014. (Photo by Dmitry Neymyrok/Reuters)

Ukrainian soldiers are seen atop armoured vehicles at a Ukrainian Army military camp set up on a field close to the Russian border in east Ukraine March 24, 2014. (Photo by Yannis Behrakis/Reuters)

A motorist checks his car next to a tank position close to the Russian border near the Ukrainian city of Kharkiv March 24, 2014. (Photo by Dmitry Neymyrok/Reuters)

A Ukrainian soldier stands guard outside a Ukrainian Army military camp set up on a field close to the Russian border in east Ukraine March 24, 2014. (Photo by Yannis Behrakis/Reuters)