A pro-Russian rebel aims his rifle at a checkpoint near a Ukrainian airbase in Kramatorsk, eastern Ukraine May 2, 2014. Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two ... more 
A pro-Russian rebel aims his rifle at a checkpoint near a Ukrainian airbase in Kramatorsk, 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 in what Moscow called a "criminal" assault by Kiev that wrecked hopes of peace. REUTERS/Marko Djurica (UKRAINE - Tags: POLITICS CIVIL UNREST) less 
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Reuters | Photo By MARKO DJURICA / REUTERS
Fri, May 2, 2014 7:04 AM EDT