As the leaders condemned the fighting and urged both sides to observe the truce, there was strident opposition from the separatists and Moscow to a plea from Ukraine for international peacekeepers to enforce the ceasefire.
The Ukrainian army, meanwhile, said 90 troops had been captured and 82 were still missing after the rebels seized the strategic town of Debaltseve, in violation of the ceasefire which came into force after midnight Sunday.
The insurgents claimed to have captured as many as 300 government soldiers.
One of the rebel leaders, Alexander Zakharchenko, alleged that 3,000 to 3,500 troops died in the assault, although such casualty counts on both sides are often greatly exaggerated for propaganda effect.
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"Let Kiev take their dead," he said.
Kiev's defeat in Debaltseve, which has had many Ukrainians questioning the competence of their military leaders, prompted Ukrainian President Petro Poroshenko to appeal for international peacekeepers to be deployed in the east.
He found little apparent support, however, with none of the others mentioning it in statements from their offices, and Moscow denying it was mentioned at all.
Instead, the four called for the implementation of the full package of measures agreed in Minsk, including a full ceasefire, withdrawal of heavy weapons and the release of prisoners, according to the French presidency.
They also called for observers from the Organisation for Security and Cooperation in Europe (OSCE) to be able to carry out their task of monitoring the ceasefire.
Journalists have also been prevented from getting into the war-ravaged town.
An AFP reporter about four kilometres (over two miles) from Debaltseve today saw rebels firing Grad rockets for 15 minutes, making the earth tremble.