The leaders of Russia, Germany and Ukraine have agreed on "concrete measures" to allow Organisation from Security and Co-operation in Europe (OSCE) observers to monitor the shaky ceasefire in Ukraine, Berlin announced.

A German government spokesman announced the measures on Tuesday morning after German Chancellor Angela Merkel, Russian President Vladimir Putin and Ukraine President Petro Poroshenko held a conference call.

"The German Chancellor and Ukrainian President called on the Russian President to exercise his influence on the separatists to enforce the ceasefire," German government spokesman Steffen Seibert said in a statement.

"Further, the withdrawal of heavy weapons should be started on Tuesday, as agreed in Minsk," he added.

Fighting subsided in many parts of eastern Ukraine under a ceasefire deal reached last week in talks involving the leaders of France, Germany, Russia and Ukraine.

But the truce appears to have been stillborn in Debaltseve, where the most intensive fighting has taken place in recent weeks.

Separatists' 'moral' fight

Despite the overnight telephone call between the leaders, pro-Russian separatists said on Tuesday that they cannot "morally" stop fighting for the town of Debaltseve because it is "internal territory".

Denis Pushilin, a rebel representative, told the Reuters news agency on Tuesday that they must respond to fire from Ukrainian troops.

"We do not have the right [to stop fighting for Debaltseve]. It's even a moral thing. It's internal territory," Pushilin said in the rebel stronghold of Donetsk.

"We have to respond to fire, to work on destroying the enemy's fighting positions ... We are ready at any time [to start the removal of heavy weapons], we have everything ready for a mutual withdrawal. We will not do anything unilaterally - that would make our soldiers targets." 

On Monday, Ukrainian military spokesman Vladyslav Seleznyov told the AFP news agency that "there is no question at the moment of us withdrawing heavy weapons" from the front line, blaming the rebels of ignoring the truce.

Source: Agencies