Foreign ministers from Russia and Ukraine meeting in the German capital Berlin have reached an agreement on a dividing line from where both sides should pull back their heavy weapons.
Germany's foreign minister, who hosted a meeting of his counterparts from Russia, Ukraine and France, said on Wednesday the four parties had agreed that the demarcation line defined in the Minsk agreement of last year should form the basis for the withdrawal.
Under the plan, Ukraine and the pro-Russian separatists would pull back their heavy arms 15 kilometres on either side of the line, though there was no agreement on a withdrawal of all troops.
"Today we have finally agreed that the demarcation line mentioned in the Minsk agreement is the line from where the withdrawal of heavy weapons needs to take place now," German Foreign Minister Frank-Walter Steinmeier told reporters after the meeting in Berlin.
Steinmeier said the agreement had been "difficult work" and the talks, which follow a fruitless round of negotiations last week, were "testing the patience of all involved".
The parties also agreed that the contact group of Ukraine, Russia, and the OSCE should meet as soon as possible with the aim of laying further groundwork for a high-level meeting in Kazakhstan's capital Astana aimed at reaching a long-lasting settlement.
Earlier on Wednesday, Russian Foreign Minister Sergey Lavrov Lavrov had urged measures to contain the unfolding unrest, but said nothing about the rebels surrendering territory they acquired in violation of a peace deal concluded in September in Minsk, Belarus.
Ukraine says separatist forces that are backed by Russia have overstepped agreed-upon front-line boundaries between the warring sides by 500 square kilometres.
A fresh separatist advance is under way in an area northwest of Luhansk, the second-largest rebel-held city. The fighting is centered on two checkpoints along a strategic highway.
Ukraine and the West accuse Russia of providing material support to the separatists, which Moscow denies. The sheer amount of sophisticated heavy weaponry in the hands of the rebels, however, is widely seen as overwhelming evidence of direct involvement by Russia.
Russia military support 'doubled'
Speaking during a visit to Kiev, US army commander Ben Hodges said the quantity of Russian equipment being provided to separatists had doubled between the September cease-fire deal and December.
"It is very clear from the capabilities that the proxies (rebels) have used against Ukrainian security forces, the type of artillery, modern equipment, the amount of ammunition that has been used," Hodges said. "It is irrefutable that they are getting direct support from Russia."
Addressing the World Economic Forum in Davos, Switzerland, Ukrainian President Petro Poroshenko held up a piece of a bullet-riddled bus as evidence of deadly shelling last week by Russian heavy artillery in his country. He has said 9,000 Russian troops are occupying seven percent of Ukrainian territory.
"For me this is a symbol, a symbol of the terroristic attack against my country," he said, comparing it to the downing of Malaysia Airlines Flight 17 over rebel-held eastern Ukraine last summer. He called it a "global problem," extending far beyond just Ukraine's borders, cutting short his visit to Davos to deal with the crisis in his country.
The fighting in the Luhansk region follows intense clashes over the weekend for control of the airport on the fringes of the main rebel city, Donetsk. The terminal - once the pride of the city but now reduced to a burned-out shell - is of limited strategic value.
Now, however, it has acquired symbolic value because of the Ukrainian forces' stand against waves of separatist attacks.
The fierce airport battle shattered the relative tranquility that had been in place since a new truce was reached in early December.
US Secretary of State John Kerry said the US was also concerned that the separatists were attacking the town of Debaltseve, about 70 kilometres east of Donetsk.
"This is a very blatant land grab and it is in direct contravention to the Minsk Agreement that they signed up to," Kerry said.