He spoke at a military camp in Sviatohirsk, a town in the eastern Donetsk region only a few kilometres from the conflict zone. It was the first time Mr Poroshenko visited the area since assuming office two weeks ago. The truce is the first step in a 14-point peace plan that also includes an amnesty and a pledge for constitutional reform. "It is not a truce invitation but an ultimatum to south-eastern militia to lay down arms," the Kremlin said in a statement that also criticised the peace plan for lacking a proposal on starting negotiations, according to the Interfax news agency. "No one will lay down their arms," said Miroslav Rudenko, a separatist leader in the self-proclaimed Donetsk People's Republic. Other rebels said they did not believe the government's truce announcement.

"We have heard of a hundred cease-fires on the part of the National Guard and the Ukrainian army. But the military operations have not stopped for a minute," said Alexander Purgin, another separatist leader in Donetsk. Ukrainian forces have kept up pressure on insurgents' positions in the Donetsk region, where the separatists blockaded access to their stronghold of Sloviansk, according to local news reports. Twelve Ukrainian soldiers were killed and 25 injured in a battle with separatists in the region late Thursday, authorities confirmed. A Ukrainian Defence Ministry spokesman, Vladislav Seleznyov, added that some 200 separatists had been killed in the fighting late Thursday close to the city of Artemivsk. The claim - which he made on his Facebook, citing preliminary figures - could not be verified independently. There were also reports of fresh fighting between insurgents and government troops along the border with Russia.

An unnamed spokesman of the "Luhansk People's Republic" told Russia's Interfax news agency that there had been fighting with government forces at three border crossings. Ukrainian border guards have in recent weeks surrendered a number of frontier posts after attacks by separatist forces. The government in Kiev accuses Russia of facilitating the entry of arms and volunteer fighters through the porous border. Poroshenko has said that securing the border with Russia is a vital condition for the peace plan's implementation. Meanwhile, Russia denied Western claims that it was amassing troops along the border with Ukraine. Kremlin spokesman Dmitry Peskov said that he was surprised by such reports and that Moscow had only beefed up border security, news agencies reported.

He added that President Vladimir Putin had ordered the reinforcements weeks ago in order to prevent border violations. "This was met with positive reactions from European leaders," Peskov said. NATO said on Thursday that it had evidence that Russia was reinforcing its troops. Germany on Friday praised Mr Poroshenko's peace plan and criticised Russia. Government spokesman Steffen Seibert said in Berlin that the reported troop movements are "definitely not a de-escalation". He added that "the willingness to make peace is only coming from one side, and we wish it came from the other side too".

European Commission President Jose Manuel Barroso said in Brussels that Poroshenko's plan was "a welcome development that should be seized by all to de-escalate the situation". The crisis in Ukraine is expected to dominate a meeting of EU foreign ministers on Monday and a summit of the bloc's leaders next Friday. EU diplomats said Friday that further sanctions against Russia remain an option as part of the push for a political solution. The United States on Friday issued sanctions against seven Ukrainian separatists, including the self-proclaimed mayor of Sloviansk, Vyacheslav Ponomaryov. Mr Ponomaryov, who reportedly has been arrested, is on the sanctions list for declaring a "take-no-prisoners" approach against Ukrainian security forces and issuing orders to "kill them all," the US Treasury said.