DONETSK, Ukraine (AFP) - A ceasefire agreed between Ukrainian forces and pro-Russian rebels came into force on Sunday, the first step in a fragile peace plan aimed at ending 10 months of conflict in east Ukraine.

The truce officially started at midnight Ukraine time (6am Sunday, Singapore time) but surging fighting in the run-up to the ceasefire has already cast doubt on whether it will be respected.

Under the terms of the deal, inked Thursday after marathon talks in Minsk between the leaders of Ukraine, Russia, Germany and France, the two warring sides have two days from the start of the truce to start pulling back heavy weapons from the front line.

The last-ditch peace plan is seen as the best hope of ending the violence that has claimed at least 5,480 lives since April but scepticism remains high after the collapse of a similar previous deal.

Ferocious fighting raged in the hours before the ceasefire was set to come into effect, with Ukraine and the United States accusing Russia of piling in weapons to fuel a rebel onslaught to grab territory.

German Foreign Minister Frank-Walter Steinmeier warned Saturday of dire consequences for Europe if the Ukraine ceasefire fails.

"If we fail now in our efforts, all parties involved in the region... will pay a high price," Steinmeier said during a visit to Lima.

"I call on the warring parties to act sensibly and avoid further escalation."