BRUSSELS (AFP) - German Foreign Minister Frank-Walter Steinmeier said it was not certain a four-way Ukraine peace summit on Wednesday in Minsk will go ahead, with much work still to be done.

"We hope that the open points can be settled but I have to say again, it is not yet sure," Steinmeier told reporters in Brussels of the summit of French, German, Russian and Ukraine leaders.

Russian President Vladimir Putin had warned that a "number of points" still needed to be hammered out before the meeting could take place.

Meanwhile, German Chancellor Angela Merkel was Monday to discuss a European-brokered peace initiative with US President Barack Obama in the latest leg of a frantic diplomatic push to stop the conflict escalating as the White House mulls supplying weapons to Kiev.

The latest peace bid is being billed as a last-ditch effort to halt the spiralling bloodshed in east Ukraine that has already cost at least 5,400 lives.