Ukraine's state border service said there had been attacks on its posts in the Luhansk region on Sunday. A spokesman for the separatists said Ukrainian forces were firing mortars at a village near the Russian frontier.

A seven-day ceasefire was declared by the Ukrainian government and began on Friday night but there have been reports of sporadic fighting in the east of the country throughout the weekend. In the Donetsk region, pro-Russian separatists reported a shootout with Ukrainian troops in Siversk, north of the city of Donetsk.

On Sunday, both the Ukrainian and Russian presidents marked the anniversary of the June 1941 invasion of the Soviet Union by Nazi Germany. It was the largest German military operation of the Second World War.

After laying flowers at the Tomb of the Unknown Soldier in Moscow, President Vladimir Putin said: "Unfortunately, what we are seeing ... tells us that the fighting is still going on and last night we saw some active use of artillery from the Ukrainian side."

But Putin also repeated his call for dialogue: "That President Poroshenko announced a truce is without a doubt an important part of a final settlement, without which no agreement can be reached, and there is no doubt that Russia will support this intention, but in the end the most important thing is a political process," the Russian president said.

France, Germany urge talks

After announcing his 15-point peace plan on Friday, Ukraine's President Petro Poroshenko also stressed the need for dialogue. He said in Kyiv on Sunday his plan "was specifically put together to ensure peace, the laying down of weapons and to establish, through talks, a single united state."

As part of his plan, Poroshenko suggested a decentralization of power to give the regions more political authority, new local and parliamentary elections and measures to protect the language rights of Russian speakers in the east.

Both German Chancellor Angela Merkel and French President Francois Hollande urged Putin by telephone on Sunday to work for a resumption of talks to end the conflict "After the Russian government too referred to the cease-fire in positive terms, the interlocutors emphasized the need for all sides to abide by it now and for a political dialogue to be put in motion," Merkel's office said in a statement. "Another topic of the conversation was the issue of securing the Ukrainian-Russian border."

Ukraine is to formally sign its association agreement with the European Union next Friday, June 27.

jm/pfd (Reuters, AP, AFP)