ARTEMIVSK, Ukraine — Ukrainian soldiers were forced to fight their way out of the embattled town of Debaltseve in the early hours of Wednesday, casting further doubt on the credibility of a days-old cease-fire and eroding the promise of ending a war in Europe that has killed more than 5,000 people.

It was unclear Wednesday how many of the thousands of Ukrainian soldiers trapped in the eastern Ukrainian town had survived the hellish retreat under enemy fire and avoided capture. President Petro O. Poroshenko put the figure at 80 percent, but since the Ukrainian military has never commented on its troop strength, the final accounting may never be known.

By midday on Wednesday, as limping and exhausted soldiers began showing up in Ukraine-held territory, it became clear that the Ukrainian forces had suffered major losses, both in equipment and human life.

“Many trucks left, and only a few arrived,” said one soldier, who offered only his rank, sergeant, and first name, Volodomyr, as he knelt on the sidewalk smoking. “A third of us made it, at most.”