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. President Vladimir Putin's spokesman said the Kremlin was "extremely worried" that it had not heard from an envoy Putin had sent to the eastern city to help free foreign hostages. He said the "punitive operation" mounted by Ukrainian forces had destroyed a peace plan agreed with Western powers two weeks ago. The Ukrainian Defence Ministry said in a statement that two Mi-24 helicopter gunships were ... (full story)