Pro-Russian militants take a break at a checkpoint close to where shelling continued Sunday between pro-Russian forces and the Ukrainian army in the village of Olenivka, some 30 kms south of Donetsk on the way to Mariupol, eastern Ukraine. Philippe Desmazes/AFP/Getty Images hide caption

itoggle caption Philippe Desmazes/AFP/Getty Images

A convoy of Russian trucks crosses the Ukrainian border at the Donetsk-Izvarino custom control checkpoint as Ukrainian refugees look on, Saturday. Russia says the trucks are carrying aid; Ukrainian officials say they don't know what's inside. SERGEI VENYAVSKY/AFP/Getty Images hide caption

itoggle caption SERGEI VENYAVSKY/AFP/Getty Images

People wait for a bus in the empty streets of Donetsk on Tuesday. The city's population, which was 900,000, is now down to around 300,000. It is beginning to return to normal following a cease-fire, which was signed last week and is mostly holding. But residents are divided over the region's future. Spencer Platt/Getty Images hide caption

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Many students at Kiev's Lyceum for the Humanities have relatives in Russia or parts of eastern Ukraine controlled by separatists. The conflict has divided families and caused many problems, they say, but it has also strengthened their sense of Ukraine's identity. Eleanor Beardsley/NPR hide caption

itoggle caption Eleanor Beardsley/NPR

A Ukrainian army checkpoint burns on the road to Russia after loud explosions were heard on the outskirts of Mariupol late Saturday. Philippe Desmazes/AFP/Getty Images hide caption

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President Obama stands alongside British Prime Minister David Cameron, center left, NATO Secretary General Anders Fogh Rasmussen, second left, Croatian President Ivo Josipovic, left, Romanian President Traian Basescu, right, and RAF Group Captain David Bentley, second right, during a flypast at the NATO summit at the Celtic Manor Resort in Newport, Wales on Friday. Jon Super/AP hide caption

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Customers shop for produce at the Danilovsky Market in Moscow. The food import ban prevents the import of almost all fresh food from the U.S., Europe and other Western countries. What's left in the market is grown locally or by Russian allies. Karoun Demirjian hide caption

itoggle caption Karoun Demirjian

President Obama sits with (from left) French President Francois Hollande; Ukrainian President Petro Poroshenko; British Prime Minister David Cameron; German Chancellor Angela Merkel; and Italian Prime Minister Matteo Renzi as they meet about Ukraine Thursday at the NATO summit at Celtic Manor in Newport, Wales. Charles Dharapak/AP hide caption

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A man walks past burnt vehicles near a railway station after recent shelling in Donetsk, eastern Ukraine, Aug. 29. Maxim Shemetov/Reuters/Landov hide caption

itoggle caption Maxim Shemetov/Reuters/Landov

Russian Foreign Minister Sergei Lavrov called Monday for a cease-fire in Ukraine, but demanded that Ukrainian troops leave positions from which they can "harm the civilian population." His comments come ahead of talks in Minsk, Belarus, involving Ukraine, Russia, Russia-backed separatists and international monitors. Jia Yuchen/Xinhua /Landov hide caption

itoggle caption Jia Yuchen/Xinhua /Landov