The Ukrainian girlfriend of murdered Russian opposition activist Boris Nemtsov, who was by his side when he was shot dead, has complained to police of receiving death threats, Ukrainian prosecutors said on Friday.

"Ganna Duritska... filed a statement about the threat to her life from unidentified people during her time in her parents' home" where she has stayed since her return Monday to Kiev from Moscow, said a statement from the prosecutor general. 

Rescuers found 32 bodies of miners in the Zasyadko mine in eastern Ukraine a day after a blast ripped through the shaft, a rebel official said on Thursday.

"32 bodies of dead miners of the Zasyadko mine have been found" by early morning, the emergency ministry of the self-proclaimed Donetsk People's Republic said in a statement, adding that the bodies were being raised to the surface.

At least 10 miners were killed and 23 more were missing and feared dead in eastern Ukraine after a blast on Wednesday at an accident-prone coal mine in the rebel-held city of Donetsk.

The early morning blast, believed to be caused by a build-up of methane gas, hit the Zasyadko mine near the city's bomb-scarred airport in what officials described as a "terrible tragedy".

A plea from Ukraine for international peacekeepers to enforce a shattered ceasefire in the east ran into strident opposition Thursday from pro-Russian rebels and Moscow.

They argued the appeal, made late Wednesday by Ukrainian President Petro Poroshenko, sought to "destroy" the U.N.-backed truce agreed under European mediation last week in the Belarus capital Minsk.

Ukrainian forces have come under fire from pro-Russian rebels over 100 times in the last 24 hours, despite a ceasefire coming into force at midnight on Saturday, Ukraine's Foreign Minister Pavlo Klimkin said Monday.

"We and the Ukraine armed forces are fully observing the ceasefire regime but unfortunately in response we have received 112 fire attacks in the past 24 hours from the terrorists of Donetsk and Lugansk," Klimkin said during a visit to Sofia.

"I couldn't care less whether we're under the Ukrainians or the separatists. I just want peace," Irina, a war-weary doctor in rebel-controlled eastern Ukraine, said as shelling boomed close to her hospital.

Irina, who declined to give her surname, said she had backed the pro-Western government that came to power after the ouster of pro-Russian president Viktor Yanukovych a year ago.

Shelling at a hospital in east Ukraine killed four people on Wednesday ahead of a visit to Kiev by U.S. Secretary of State John Kerry that will see possible arms supplies high on the agenda.

The latest deaths came as international pressure grew for an immediate halt to surging violence which has seen hundreds of civilians killed in recent weeks as pro-Russian rebels pushed into government-held territory.

Truce talks between Ukraine's government and pro-Russian insurgents appeared to collapse Friday after 24 people, mostly civilians, were reported killed in heavy weapons fire in eastern Ukraine, prompting new European criticism of Russia.

Plans for the talks in the Belarussian capital Minsk were announced on Thursday, raising hopes of dialogue amid the collapse of a September truce in a war that has killed at least 5,100 people, according to the United Nations.

Fighting in eastern Ukraine has killed three soldiers, officials said Saturday, as an upsurge in clashes in recent days between the army and pro-Russian rebels centred around control of a battered airport.

Further battles shook the area around the Donetsk airport on Saturday, with Ukraine's military saying it was defending its positions despite rebel claims that they had taken control of the site.

The death toll from a stray rocket that hit a Ukrainian bus climbed to 12 on Wednesday as Moscow and Kiev traded blame for the separatist war's bloodiest incident since a September truce.

The long-range Grad rocket exploded on Tuesday near a commuter bus traveling towards the pro-Russian rebel stronghold of Donetsk from Ukraine's southeast coast.