French, German and Ukrainian leaders are planning a summit with Russian President Vladimir Putin on Wednesday in a frantic bid to halt escalating bloodshed in east Ukraine.

The four leaders talked by phone on Sunday as part of efforts to achieve a "comprehensive settlement" in the conflict between Ukrainian forces and pro-Russian rebels, Berlin said.

German Chancellor Angela Merkel and French President Francois Hollande have been carrying out frantic diplomacy in recent days, jetting to Kiev for talks with Ukrainian President Petro Poroshenko and to Moscow to meet Putin, who is accused by the West of being behind the 10-month conflict.

Putin said the summit planned in the Belarussian capital Minsk would only take place if the leaders agreed on a "number of points" by then.

"We will be aiming for Wednesday, if by that time we manage to agree on a number of points which we've been intensely discussing lately," Putin told Belarussian President Alexander Lukashenko.

Foreign ministry officials will hold preparatory talks in Berlin on Monday, Ukraine said, when Merkel meets  President Obama. A meeting between mediators from the Organization for Security and Co-operation in Europe, Ukrainian and Russian representatives and rebels is also expected to occur Tuesday, Ukraine's presidency said.

During the latest push to keep peace hopes alive, the leaders "continued to work on a package of measures to achieve a comprehensive settlement of the conflict in eastern Ukraine," Berlin said of Sunday's phone conversation about what Hollande has called "one of the last chances" for peace.

The Ukrainian presidency said the leaders "expect that their efforts during the Minsk meeting will lead to an immediate and unconditional bilateral ceasefire." Fresh fighting in the former Soviet republic claimed 12 civilian lives, separatist and Kiev authorities said, with 12 Ukrainian troops also killed in the last 24 hours. A peace deal agreed in Minsk in September has since been largely ignored, with fighting escalating in recent weeks and the Ukrainian government accusing the rebels of massing troops for fresh offensives.

French Foreign Minister Laurent Fabius told the Munich Security Conference that "what Germany and France are seeking right now is not peace on paper, but peace on the ground."

With the US seemingly thinking of arming Ukrainian troops despite some European opposition, US Secretary of State John Kerry insisted that the US and Europe remained united.