MOSCOW — With the accord they brokered last week to end the conflict in eastern Ukraine seemingly in tatters, the leaders of Russia, Ukraine, Germany and France spoke by telephone on Thursday in an effort to find a way to impose a so-far elusive truce.
The call came a day after President Petro O. Poroshenko of Ukraine ordered a withdrawal of forces from Debaltseve, a strategically important transport hub that was captured by Russian-backed separatist forces in intense fighting that continued for days after the cease-fire formally took effect last weekend.
None of the provisions of the peace accord, forged during an overnight negotiating session in Minsk, Belarus, have yet been carried out in line with the terms and timetable.
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Highlighting its control over Debaltseve, Russia said on Thursday that it was sending a convoy of humanitarian aid to the town.
Mr. Poroshenko’s office said that at least six Ukrainian soldiers had died during the retreat from Debaltseve on Wednesday and that more than 100 were injured, though reports from soldiers on the ground suggested the numbers could be substantially higher.
In a statement defending his decision to order the withdrawal, Mr. Poroshenko said that 2,475 soldiers were safely pulled out, along with 200 military vehicles.
