Fighting intensifies in eastern Ukraine

Separatists down two helicopters as Kiev launches offensive to retake city

Pro-Russian rebels shot down two Ukrainian helicopters on Friday, killing two crew members, as government troops tightened their siege of separatist-held Sloviansk. Ukraine's acting president Oleksander Turchinov claimed "many" pro-Russia insurgents were killed or wounded.

Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace.