Ukrainian soldiers stand in front of pro-Russian civilians (not in picture) at a checkpoint near the town of Slaviansk
Ukrainian soldiers stand in front of pro-Russian civilians (not in picture) at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
A Ukrainian soldier stand in front of Pro-Russian Civilians at a checkpoint near the town of Slaviansk in eastern Ukraine
A Ukrainian soldier stands in front of Pro-Russian Civilians at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
Ukrainian soldiers stand guard near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine
Ukrainian soldiers stand guard near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
A Ukrainian soldier stand in front of Pro-Russian Civilians at a checkpoint near the town of Slaviansk in eastern Ukraine
A Ukrainian soldier stands in front of Pro-Russian Civilians at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
Ukrainian soldiers stand with an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine
Ukrainian soldiers stand with an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
A Ukrainian soldier stand in front of Pro-Russian Civilians at a checkpoint near the town of Slaviansk in eastern Ukraine
A Ukrainian soldier stands in front of Pro-Russian Civilians at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST)
Ukrainian soldiers stand with an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine
Ukrainian soldiers stand with an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
A Ukrainian soldier stands guard near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine
A Ukrainian soldier stands guard near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
Ukrainian soldiers stand near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine
Ukrainian soldiers stand near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)
A Ukrainian soldier stands guard near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine
A Ukrainian soldier stands guard near an armoured personnel carrier at a checkpoint near the town of Slaviansk in eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew, as troops tightened their siege of separatist-held Slaviansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace. REUTERS/Baz Ratner (UKRAINE - Tags: POLITICS CIVIL UNREST MILITARY)