A ceasefire agreed between Ukrainian forces and pro-Russian rebels has come into force, 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 (0900 AEDT Sunday), but surging fighting in the run-up to the ceasefire has already cast doubt on whether it will be respected.

However it envisages the creation of a neutral “buffer zone” and withdrawal of the heavy weapons responsible for many of the 5,000 casualties in the conflict that broke out almost a year ago.

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“As of the morning of February 15, there have been 10 shelling attacks on our positions by rebels – mainly in the area of Debaltseve,” spokesman Anatoly Stelmach said by telephone.

Debaltseve is seen as the more likely potential flashpoint for violence, as pro-Russian rebels battled fiercely to surround Ukranian forces in the hours leading up to the truce, which came into effect at midnight on Sunday (local time).

A Reuters witness in east Ukraine heard the sound of heavy artillery fire coming from the direction of Debaltseve, a key transport hub.

Separatist news service DAN quoted a senior rebel commander as saying rebels had opened fire in defence, after Ukrainian forces had violated the ceasefire around Debaltseve.

“Units were forced to open fire in response,” Eduard Basurin was quoted as saying.

Elsewhere, an elderly man and woman died after Grad missile fire hit the town of Popasna in the Lugansk region around 20 minutes after the start of the ceasefire, a local official said.

Another military spokesman, Vladyslav Seleznyov, said the ceasefire was being observed in general.

“Shelling [by rebels] has been not regular and [has been] localised,” he said.

Under the terms of the deal, inked on 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 frontline.

However, Ukrainian president Petro Poroshenko warned the peace process in Ukraine was being “threatened” by separatists.

“Unfortunately, the peace process is threatened, the rebels will use Debaltseve to undermine the ceasefire,” Mr Poroshenko said.

“As supreme commander of the armed forces, I want peace.”