PARIS, Feb. 24 - Talks about a fragile peace deal for Ukraine ended in tension Tuesday, with differences over who is at fault over continued violence despite a cease-fire, the AP reported.

The foreign ministers of Russia, Ukraine, Germany and France met in Paris amid uncertainty that the accord will hold — in particular a promised withdrawal of heavy weapons from the front line.

Ukraine delayed the pullout Monday, blaming continuing attacks from separatist rebels in eastern Ukraine.

German Foreign Minister Frank-Walter Steinmeier described the talks as difficult.

Ukrainian Foreign Minister Pavlo Klimkin emerged grim-faced, saying they agreed on some "technical aspects" including more support for an OSCE monitoring mission — but didn't reach an agreement on condemning recent violence in the town of Debaltseve or who is at fault for continuing sporadic violence despite a cease-fire.

Under a peace agreement reached Feb. 12 by France, Germany, Russia and Ukraine, both sides must withdraw their heavy weapons between 15 to 45 miles to create a buffer zone.

Sergey Lavrov of Russia said the discussion focused on the implementation of the peace deal.

"The most important thing is to ensure the cease-fire," he said, according to Russian news agencies.

Fabius said they want to extend the OSCE mandate. He said all four "remain determined to continue action in this format and do the utmost to ensure" that promises are kept.

A French diplomatic source told Reuters that would be discussed in the coming days in Vienna and would include providing the mission with protected vehicles and more technical surveillance means.

"If we let them work they have sufficient personnel to criss-cross the zones and carry out controls, but they just don't have access to these zones for now," he said.

Steinmeier noted there had been some signs of progress regarding agreements to withdraw heavy weaponry from conflict zones but said that should now physically take place "within the coming days.”

The French source said the withdrawal plan proposed by both Ukrainian and separatist military chiefs was deemed credible by French and German military experts.

Meanwhile, Klimkin said he feared separatists would now relocate forces toward the government-held port of Mariupol.

"It can't be perceived as a breakthrough. What we need is for the shelling to stop. We need the implementation of the Minsk accords, nothing more," he told reporters at the embassy in Paris.

The French diplomat said the next follow up meeting would take place in Berlin within 10 days at the deputy minister or political director level. (ap/rt/ez)