Separatist leaders in two main areas of Ukraine's east have agreed to observe a ceasefire until 27 June, one of them, Alexander Boroday, has said.

He was speaking after meeting a "contact group" which included a former Ukrainian president, Moscow's envoy to Kiev and a representative of the OSCE security watchdog.

Mr Boroday said: "The consultation ended with authorities of the Luhansk and Donetsk Republics agreeing to maintain a ceasefire for their part until the 27th."

Their truce will run parallel to a unilateral Ukrainian military ceasefire that was declared by President Petro Poroshenko on Friday.

The ceasefire is part of a peace plan to end an insurgency by pro-Russian separatists in the Russian-speaking east of Ukraine.

EU foreign ministers have said the 15-point plan put forward by the new Ukrainian president is an opportunity to defuse the crisis that has led to hundreds of deaths and caused a confrontation between Russia and the West.

They called on Russia to "support the peace plan and to adopt effective measures to stop the continued flow of illegal fighters, arms and equipment over the border into Ukraine".

A statement from the ministers, who met in Luxembourg, noted the EU has been drawing up further sanctions that could be imposed on Russia if events in eastern Ukraine required it.

But ministers' comments again showed divisions among the EU's 28 member states about pushing ahead with tough economic sanctions against Russia they have been threatening since March.

British Foreign Secretary William Hague said EU leaders would weigh Russia's actions at a summit on Friday.

He warned Russia that the EU was ready to impose tougher sanctions if it was not satisfied with Moscow's response to Kiev's peace plan.

"[Russian President Vladimir] Putin should be in no doubt that in the EU we are ready to take those measures," he said.

But Dutch Foreign Minister Frans Timmermans said that whether EU leaders adopted more sanctions against Russia on Friday depended on developments between now and then.

"I think the need is to stimulate all parties to negotiate and try and avoid the need to escalate the sanctions. I hope that we can avoid that step," he said.

EU foreign ministers also agreed to ban imports from Crimea, reiterating that the EU would never recognise Russia's "illegal" annexation of Ukraine territory.

US President Barack Obama today warned Mr Putin that Russia would face new sanctions if it failed to both stop the flow of weapons into Ukraine and halt support for separatists.

The White House said that Mr Obama delivered the warning in a telephone call with the Russian leader, in which he called for "concrete actions" by Moscow to de-escalate the situation.

The Kremlin said in its own statement that Mr Putin stressed the need for a true ceasefire in Ukraine and direct talks for the warring parties.

It was the first time that Mr Putin and Mr Obama had spoken since they met at D-Day 70th anniversary celebrations in Normandy, France on 6 June.