A Ukrainian military helicopter flies near a Ukrainian checkpoint near the town of Slaviansk
A Ukrainian military helicopter flies near a Ukrainian checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukrainian forces attacked the rebel-held city of Slaviansk before dawn on Friday and pro-Russia separatists shot down at least one attack helicopter, killing a pilot, in a sharp escalation of the conflict. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
Civilians talk with Ukrainian troops at a checkpoint near the town of Slaviansk
Civilians talk with Ukrainian troops at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukrainian forces attacked the rebel-held city of Slaviansk before dawn on Friday and pro-Russia separatists shot down at least one attack helicopter, killing a pilot, in a sharp escalation of the conflict. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
A man shakes hands with Ukrainian troops at a checkpoint near the town of Slaviansk
A man shakes hands with Ukrainian troops at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukrainian forces attacked the rebel-held city of Slaviansk before dawn on Friday and pro-Russia separatists shot down at least one attack helicopter, killing a pilot, in a sharp escalation of the conflict. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
A woman stands with an Orthodox icon at a Ukrainian checkpoint near the town of Slaviansk
A woman stands with an Orthodox icon at a Ukrainian checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukrainian forces attacked the rebel-held city of Slaviansk before dawn on Friday and pro-Russia separatists shot down at least one attack helicopter, killing a pilot, in a sharp escalation of the conflict. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST RELIGION TPX IMAGES OF THE DAY)
A pro-Russian separatist stands guard on top of an armoured personnel carrier in the town of Slaviansk
A pro-Russian separatist stands guard on top of an armoured personnel carrier in the town of Slaviansk in eastern Ukraine May 2, 2014. Ukraine launched a "large-scale operation" to retake the eastern town of Slaviansk, pro-Russian separatists there said on Friday, in an escalation of violence in what has become the worst confrontation between Russia and the West since the Cold War. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
A pro-Russian separatist stands guard near an armoured personnel carrier in the town of Slaviansk
A pro-Russian separatist stands guard near an armoured personnel carrier in the town of Slaviansk in eastern Ukraine May 2, 2014. Ukraine launched a "large-scale operation" to retake the eastern town of Slaviansk, pro-Russian separatists there said on Friday, in an escalation of violence in what has become the worst confrontation between Russia and the West since the Cold War. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
A pro-Russian separatist guards a checkpoint as tyres burn in front of him, near the town of Slaviansk
A pro-Russian separatist guards a checkpoint as tyres burn in front of him, near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukraine launched a "large-scale operation" to retake the eastern town of Slaviansk, pro-Russian separatists there said on Friday, in an escalation of violence in what has become the worst confrontation between Russia and the West since the Cold War. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
Pro-Russian separatists guard a checkpoint near the town of Slaviansk
Pro-Russian separatists guard a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukraine launched a "large-scale operation" to retake the eastern town of Slaviansk, pro-Russian separatists there said on Friday, in an escalation of violence in what has become the worst confrontation between Russia and the West since the Cold War. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
A pro-Russian separatist guards a checkpoint as tyres burn behind him near the town of Slaviansk
A pro-Russian separatist guards a checkpoint as tyres burn behind him near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukraine launched a "large-scale operation" to retake the eastern town of Slaviansk, pro-Russian separatists there said on Friday, in an escalation of violence in what has become the worst confrontation between Russia and the West since the Cold War. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
A pro-Russian separatist guards a checkpoint as tyres burn behind him, near the town of Slaviansk
A pro-Russian separatist guards a checkpoint as tyres burn behind him, near the town of Slaviansk in eastern Ukraine May 2, 2014. Ukraine launched a "large-scale operation" to retake the eastern town of Slaviansk, pro-Russian separatists there said on Friday, in an escalation of violence in what has become the worst confrontation between Russia and the West since the Cold War. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)