Fighting flared between Ukrainian and pro-Moscow separatist forces, both sides reported, further straining a unilateral ceasefire declared by Ukraine as Russian President Vladimir Putin pressed Kiev to talk to the rebels.
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 ceasefire came under pressure almost as soon at it began on 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," 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.