Kiev (AFP) - Three Ukrainian soldiers died when a mine exploded in the separatist-held east where isolated clashes continue to undermine a ceasefire aimed at ending a year-long war.

Army spokesman Andriy Lysenko said Saturday that "as a result of the explosion of an enemy mine ... three Ukrainian soldiers were killed, two injured" in the previous 24 hours.

There were no further details on the incident which occurred near the government-held village of Avdiyivka, a few kilometres from the separatist bastion of Donetsk, a city in Ukraine's industrial heartland which prior to the unrest was home to a million people.

The fatalities were the first announced by the Kiev government in almost a week since the death of a Ukrainian army soldier was reported Monday.

Lysenko said the previous day the army had noted "the use at least five times of heavy weapons by illegal armed groups against our positions," including conventional artillery and 122-mm mortars.

Observers say a February ceasefire between the two sides is largely holding but skirmishes continue around Donetsk and the strategic port of Mariupol, Kiev's largest remaining stronghold in the rebel-held east.

The ceasefire provides for heavy weapons of over 100-mm calibre to be withdrawn along the front line to set up a buffer zone some 50 to 140 kilometres wide.

More than 6,000 people have been killed since fighting broke out between pro-Russian separatists and the Ukraine government a year ago.

Kiev and the West accuse Russian President Vladimir Putin of supporting the insurgency with troops, tanks and heavy weapons -- accusations he rejects.

The Organization for Security and Cooperation in Europe which is monitoring the ceasefire, agreed in the Belarussian capital Minsk, said Friday that the truce remained "somewhat fragile".

"As long as guns continue to be fired, and as long as substantial amounts of heavy weaponry continue to be concentrated in offensive and defensive positions, achieving a comprehensive and sustainable ceasefire will be difficult," said OSCE spokesman Michael Bociurkiw at a weekly briefing.

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He also warned of a growing humanitarian crisis in the east due to the lack of hospitals, power, water and schools.

"Children have nowhere to play or to learn," he said.

In a message Saturday to French President Francois Hollande and German Chancellor Angela Merkel, the separatist leaders of the self-proclaimed Donetsk and Lugansk "republics" complained that the Kiev authorities had failed to resume social benefit payments to the region as agreed in Minsk in February.

It said the Ukraine government "continues the blockade" of the region "including the banking system, depriving more than a million pensioners and leaving them without a livelihood."

"We call on you, the guarantor countries, to influence and encourage the leadership of Ukraine to ... restore social benefits to residents of Donbass," they added