MOSCOW -- Fighting flared between Ukrainian and pro-Moscow separatist forces, both sides reported Sunday, further straining a unilateral cease-fire declared by Ukraine as Russian President Vladimir Putin pressed Kiev to talk to the rebels.
Mr. Putin and Ukrainian President Petro Poroshenko, at separate ceremonies marking the anniversary of Nazi Germany's invasion of the Soviet Union, both stressed the need to bring peace to Ukraine's rebellious east.
The seven-day cease-fire came under pressure almost as soon at it began Friday night, with the government accusing the separatists of attacking its military bases and posts on the Russian border. The violence continued for a second night into Sunday.
"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," Mr. Putin said after laying flowers at the Tomb of the Unknown Soldier in Moscow.
He said it was not clear whether artillery was used by the Ukrainian army or the "so-called paramilitary of the right-wing forces" supporting the government. He appeared to attach no blame to separatist forces.
Mr. Poroshenko wants Mr. Putin's unqualified backing for a 15-point peace plan he announced Friday before meetings with the European Union in the coming week. These will include the signing Friday of an association agreement with the bloc, which includes a free trade deal.
In his comments published on the Kremlin website, Mr. Putin repeated his support for the cease-fire and peace plan in only general terms.
"It is important that this cease-fire lead to dialogue between all opposing sides in order to find compromises acceptable for all," he said.
The insurgency in the largely Russian-speaking east erupted in April after street protests in the capital Kiev toppled the Moscow-backed leader Viktor Yanukovich. Russia subsequently annexed Ukraine's Crimean peninsula, and the West has accused Russia of supporting the insurgency.
French President Francois Hollande and German Chancellor Angela Merkel reiterated to Mr. Putin by telephone Sunday "the importance of ensuring full control of the Russia-Ukraine border to prevent the infiltration of gunmen and military equipment," the statement said.
Ukraine's state border service reported further rebel attacks on its posts in Luhansk region Sunday, while a separatist spokesman said Ukrainian forces were firing mortars at a village near the Russian frontier.
In Donetsk region, which like Luhansk has declared itself a "people's republic," rebels reported a morning shootout with Ukrainian troops in Siversk, north of the city of Donetsk.