"In order to preserve the lives of Ukrainian defenders, a decision was made to withdraw," said the Ukrainian army.

Clashes have been intense in Lysychansk, the last major city in the Luhansk region still in Ukrainian hands.

"Remaining in positions that have been relentlessly shelled for months just doesn't make sense."

"They are just destroying everything," said the governor of Ukraine's Luhansk region.

The EU foreign policy chief called the Russian blockade of Ukrainian ports "a real war crime."

Ukrainian troops have been told "to surrender or die" by Russia-backed forces.

Russia said the strike on Chortkiv destroyed U.S.-supplied "anti-tank missile systems, portable air defense systems and shells.”