Kiev (AFP) - Ukraine accused pro-Russian separatists Monday of using mortars and a tank to fire on government positions near the eastern port of Mariupol in clashes that lasted several hours, violating a nearly month old ceasefire.

The militants had fired on Ukraine's positions and were attempting to "force our contingents from Shyrokyne," a village about 10 kilometres east of Mariupol on the Azov Sea coast, the headquarters of the army's operations in the east said in a Facebook post.

Mariupol, a steel-making city of 500,000, is the biggest urban centre in the conflict zone still controlled by Kiev. The frontline runs through Shyrokyne.

"Starting at 10:00 am (0800 GMT), the militants began to brazenly violate the Minsk accords, firing from 120-millimetre mortars and a tank at Ukrainian forces," said Oleg Sushinsky, a military spokesman in Mariupol, referring to the ceasefire signed in the Belarussian capital Minsk.

Four Ukrainian soldiers were wounded, he told AFP.

It was impossible to immediately verify his claims.

Use of heavy weapons would violate the February 12 Minsk deal, under which both sides were supposed to withdraw mortars, rockets and other large calibre arms from the frontlines to end fighting that has killed at least 6,000 people.

The defense minister of the self-proclaimed rebel Donetsk People's Republic, Eduard Basurin, told Russia's RIA Novosti website that rebels had not engaged in any offensive manoeuvres.

But a spokesman for the Azov volunteer battalion, which is fighting alongside government forces in Mariupol, said Shyrokyne had been the scene of sporadic clashes for several days.

The spokesman insisted that Ukraine had already removed artillery from the village, while Ilya Kiva, deputy head of government police forces in the disputed Donetsk region, said Ukrainian troops were in "very serious" trouble because of the withdrawals.

Many Ukrainians fear that any new offensive by the rebels would target Mariupol because of its strategic location and economic importance. The port was hit by a rocket attack in January that killed at least 30 civilians.

International observers trying to monitor the ceasefire and weapons withdrawal have repeatedly complained that rebels are denying them access to outlying areas of Mariupol.