President Petro Poroshenko has called for UN peacekeepers to be deployed to eastern Ukraine to enforce a ceasefire.

At an emergency security meeting, he said such a force would help guarantee security "in a situation where the promise of peace is not being kept".

His comments came after Ukrainian troops withdrew from the strategic city of Debaltseve after intense fighting.

The rebel advance on Debaltseve, which came in spite of the ceasefire agreed last week, has been widely condemned.

Mr Poroshenko's request was approved by Ukraine's national security and defence council at the emergency meeting on Wednesday night.

"The issue was discussed and a decision has been taken to appeal to the UN and the EU concerning the setting up in Ukraine of a peacekeeping and security operation," council secretary Olexander Turchynov told reporters.

The move came after President Poroshenko said almost 2,500 Ukrainian soldiers had withdrawn from Debaltseve on Wednesday.

He said the withdrawal had been organised, but that at least six soldiers were killed and more than 100 wounded.

Earlier, a senior Ukrainian military official said 22 Ukrainian soldiers had died in Debaltseve over the past three days. Rebel claims of a much higher figure have been dismissed by the government.

The ceasefire, which came into effect on Sunday, has been broadly observed elsewhere in eastern Ukraine and some heavy weaponry is said to have been withdrawn by both sides.

However, staff from the OSCE security group that is monitoring the ceasefire have been unable to reach Debaltseve.