Belarusian President Alexander Lukashenko (from left), Russian President Vladimir Putin, German Chancellor Angela Merkel, French President Francois Hollande and Ukrainian President Petro Poroshenko pose for a photo at the presidential residence in Minsk on Wednesday, during a meeting aimed at halting a 10-month war in Ukraine. Photo: AFP

Germany, France, Russia and Ukraine reached a deal on Thursday that offers a "glimmer of hope" for an end to fighting in eastern Ukraine after marathon overnight talks.

But all four leaders said there was a long way to go and accusations from Kiev of a new, mass influx of Russian armor into rebel-held eastern Ukraine further undermined the situation.

The deal envisages a cease-fire between Ukrainian forces and Russian-backed separatists starting on Sunday, followed by the withdrawal of heavy weapons from the front line and constitutional reforms to give eastern Ukraine more autonomy.

"The main thing which has been achieved is that from Saturday into Sunday there should be declared, without any conditions at all, a general cease-fire," Ukrainian President Petro Poroshenko told journalists.

Emerging separately from more than 16 hours of negotiations, the leaders differed over the reasons why the talks took so long.

Russian President Vladimir Putin accused Kiev of prolonging the talks, the culmination of a dramatic diplomatic initiative by France and Germany following an upsurge in fighting in which the rebels tore through an earlier cease-fire line.

German Chancellor Angela Merkel, on the other hand, said Poroshenko "did everything to achieve the possibility of an end to the bloodshed", while she said Putin put pressure on the rebels to agree to the cease-fire "toward the end" of the talks.

The deal offered a "glimmer of hope" she said, but big obstacles remained in the way of peace. It is likely to ease pressure in the US for Washington to send military aid to the stretched Ukrainian army, and from some in Europe for tighter sanctions against Moscow, due to be discussed at a European summit later on Thursday.

The agreement could also help protect Putin from any fallout from the deaths of Russians in the fighting, which Ukraine claimed were soldiers. Moscow says they are volunteers.

A Ukrainian military spokesman said around 50 tanks, 40 missile systems and 40 armored vehicles had crossed overnight into eastern Ukraine from Russia. Moscow dismissed this as groundless.

The fighting has destabilized Ukraine both militarily and economically. As the deal was reached, Ukraine was offered a $40-billion lifeline by the International Monetary Fund to stave off financial collapse.

The agreement addressed some of the main stumbling points, including a "demarcation line" between rebels and Ukrainian forces, which the rebels wanted to reflect gains from a recent offensive which shredded an earlier cease-fire deal.

The compromise was that the rebels will withdraw weapons from a line set by the earlier Minsk agreement in September, while the Ukrainians will withdraw from the current frontline.

Ukraine will also get control of its border with Russia, but in consultation with the rebels and only after the regions gain more autonomy under constitutional reform by the end 2015.

The cease-fire and heavy weapons pullback would be overseen by Europe-wide security body, the Organization for Security and Cooperation in Europe.

Li Xing, a professor of Russian Studies at Beijing Normal University, told the Global Times on Thursday that the Minsk agreement will, to some degree, ease tensions in Ukraine.

"It is very difficult for the four countries to reach an agreement like this. All parties have made concessions. It is a positive effort to work toward peace," Li said.

As the fighting in Ukraine escalated, Washington has begun openly talking of arming Ukraine to defend itself from "Russian aggression," raising the prospect of a proxy war in the heart of Europe between former Cold War rivals.

"The fact that the US was not directly involved in the negotiations in Minsk exposes the different views of the US and its European allies. The US is more inclined to solve the Ukraine crisis with hard-line methods while Europe wishes to adopt diplomatic means," Li noted.

"The Minsk agreement is only a temporary solution. Its long-term effect is hard to predict at the moment as the core issues of the Ukraine crisis, the split of eastern and western Ukraine and the conflict between the US and Russia on a global stage, have not been dealt with in the negotiations," Li said.