KIEV (REUTERS) -Some pro-government forces began on Wednesday to pull out of the east Ukrainian town of Debaltseve which is under siege from Russian-backed separatists, commanders of pro-government paramilitary units said.

"The withdrawal of forces from Debaltseve is taking place in a planned and organised way," said Semen Semenchenko, who heads the pro-government paramilitary battalion, Donbass.

"The enemy is trying to cut the roads and prevent the exit of the troops," he said on Facebook. Another pro-government paramilitary leader, Mykola Kolesnyk, said in a telephone interview on 112 television channel: "We have pulled out. We have saved people's lives."

But he said not all troops were pulling out.

"We are talking only about units which are surrounded in populated areas in and around the town," said Kolesnyk who heads the Krivbas battalion.

Separatist forces, who the pro-Western government in Kiev say are supported and armed by Russia, fought their way into the key railway junction on Tuesday despite a ceasefire which came into effect on Sunday but has been under pressure from the start.

Rebels say the ceasefire, negotiated by Ukraine, Russia, Germany and France at a summit in Belarus late last week, does not apply to Debaltseve, a strategic transport hub which links the two rebel-controlled regions of eastern Ukraine.

Russian President Vladimir Putin, whom Kiev and Western countries accuse of directing the rebels' tank and artillery assault on the town, told Kiev in Budapest on Tuesday that it should let its soldiers surrender.

Semenchenko, who is also a parliamentary deputy, said: "This war will not end in Debaltseve. Under cover of the Minsk agreements, Putin will destroy more and more of our people and seize our positions."

The Ukrainian Defence Ministry, in an early morning statement, said fighting was going on in the town but it was not clear if this was still going on while government forces were withdrawing.