A girl sits on railway tracks at a makeshift camp for refugees and migrants at the Greek-Macedonian border near the village of Idomeni, Greece, March 19, 2016. (Photo by Alkis Konstantinidis/Reuters)

Refugees and migrants try to find a place on an already full train headed for Serbia, near the city of Gevgelija, The Former Yugoslav Republic of Macedonia, on February 24, 2016. Refugees and migrants from Iraq and Syria continue to pass through Macedonia on their way to the European Union. (Photo by Georgi Licovski/EPA)

Indigenous Sahrawi girls play on an improvised see-saw at a refugee camp of Boudjdour in Tindouf, southern Algeria March 3, 2016. UN Secretary General Ban Ki-moon is scheduled to visit the Sahrawi refugees in south-west Algeria's Tindouf region. (Photo by Zohra Bensemra/Reuters)

Burundian refugees gather on the shores of Lake Tanganyika in Kagunga village in Kigoma region in western Tanzania with their belongings, as they wait for MV Liemba to transport them to Kigoma township, May 17, 2015. Burundi's embattled President Pierre Nkurunziza sacked his defense and foreign ministers on Monday, five days after surviving an attempted coup by generals opposed to his bid for a third term in office. (Photo by Thomas Mukoya/Reuters)

Migrants rush as they try to get on a train heading to the border with Serbia at the train station of Gevgelija, on the Macedonian-Greek border, on August 9, 2015. Non-EU Serbia's frontier with Hungary, which is in the bloc's passport-free Schengen zone, has become a major crossing point for the huge numbers of migrants entering the EU. (Photo by Dimitar Dilkoff/AFP Photo)

A woman and a child make a bonfire at a makeshift camp for migrants and refugees at the Greek-Macedonian border near the village of Idomeni, Greece, April 1, 2016. (Photo by Marko Djurica/Reuters)

A Syrian refugee girl cries as she walks through a rainstorm towards Greece's border with Macedonia, near the Greek village of Idomeni, September 10, 2015. Most of the people flooding into Europe are refes fleeing violence and persecution in their home countries who have a legal right to seek asylum, the United Nations said on Tuesday. (Photo by Yannis Behrakis/Reuters)

A migrant smokes a cigarette as he waits among others to cross the Croatian border near the village of Berkasovo, Serbia October 19, 2015. Thousands of migrants clamoured to enter European Union member Croatia from Serbia on Monday after a night spent in the cold and mud of no-man's land, their passage west slowed by a Slovenian effort to impose limits on the flow to western Europe. (Photo by Marko Djurica/Reuters)