Ukrainian President Petro Poroshenko is calling for the deployment of U.N. peacekeepers to monitor a cease-fire in eastern Ukraine, amid reports that at least 13 soldiers were killed while withdrawing from the town of Debaltseve. (Reuters)

Hopes for a cease-fire in Ukraine were fading on Thursday as fighting spread again across the war-torn east a day after a stinging defeat for government forces.

The renewal in combat from the Sea of Azov northward nearly 100 miles to the rebels’ new trophy of Debaltseve, a key railway hub, dimmed hopes for a peace deal reached last week. Rebels said Thursday they would continue to “purge” their new territory of Ukrainian soldiers, threatening further violence in the coming days.

The continued battles came as Ukraine’s government reported steeper losses than it had initially stated in a chaotic pullout from Debaltseve a day earlier. The conflict is increasingly threatening the stability of Ukraine’s government, which must explain to citizens why it allowed an entrapment that led to the bloody denouement on Wednesday. European leaders and the White House also face credibility questions, having threatened tough consequences if the peace plan failed to take hold.

Ukraine’s military said Thursday that at least 13 soldiers were killed and 92 captured on Wednesday alone. An additional 82 soldiers were missing after the pullback from Debaltseve. Prospects for their recovery were grim; many of the troops who escaped said they had left corpses behind in the retreat over the frozen Ukrainian steppe.

[Read: Ukrainian soldiers recall desperate run to safety]

Map: Cease-fire pull back lines

After the defeat, Ukrainian President Petro Poroshenko pleaded for U.N. peacekeepers to fan out across Ukraine’s border with Russia, as well as the front line between rebel and government territory. The request amounted to a stark admission that he no longer believes Ukraine can defend itself alone.

But Russian diplomats said Thursday that any such mission would derail the cease-fire agreement reached last week in the Belarusan capital, Minsk, by the leaders of Russia, Ukraine, France and Germany. Russia holds veto power on the U.N. Security Council and could scuttle any proposal for U.N. peacekeepers.

Even many Poroshenko allies questioned the handling of the operation during which thousands of Ukrainian soldiers were encircled and trapped under heavy bombardment by rebel forces. Combined with Ukraine’s grinding economic difficulties, the military debacle means Poroshenko may face an erosion of support in Kiev only eight months after taking power.

Later, Poroshenko told reporters that after the peace deal was signed, rebels and Russian forces “destroyed Debaltseve, wiping it off the face of the Earth. Today Debaltseve resembles a lunar landscape.”

Russia has denied sending its troops to eastern Ukraine in the conflict, which has cost more than 5,600 lives.

The group charged with monitoring the two sides’ compliance with the agreement said Thursday that a key part of the plan — the pullback of heavy weaponry from the front lines — did not appear to be happening, despite claims from both sides that they were doing so.

“The Minsk documents are not a shopping list; it’s one integrated whole,” said Michael Bociurkiw, a spokesman for the Organization for Security and Cooperation in Europe.

The organization said later that both sides had been using heavy weaponry on Thursday across the region.

Observers have not been allowed into Debaltseve, the scene of the hardest fighting in recent days, Bociurkiw said. Rebel leaders said Thursday that OSCE teams could soon enter — but only after the pro-Russian forces had emptied the town of pro-Ukraine holdouts.

“Tomorrow, or maximum the day after tomorrow, the purge of Debaltseve will be over. The OSCE mission will be able to visit,” said rebel military spokesman Eduard Basurin, according to Russian news agencies. If Ukrainian forces continued shelling rebel positions, the rebels would pull out of the peace deal, he warned.

Fighting flared Thursday near the key Ukrainian-held port city of Mariupol, where an eastern suburb came under heavy artillery attack by rebel forces. Witnesses in Donetsk also reported artillery fire lasting for hours.

In spite of the violence, German Chancellor Angela Merkel and French President François Hollande appeared Thursday to be clinging to hopes that the peace plan would take hold. Merkel’s office said the leaders had agreed to “hold firm to the Minsk agreements despite the grave breach of the cease-fire in Debaltseve.”

But rising discontent could be seen clearly in Ukraine after the military defeat. Borys Filatov, deputy governor of the eastern region of Dnipropetrovsk, urged Poroshenko, nominally an ally, to “live not by lies” after the president said Wednesday that only six soldiers had died in the pullout.

And Semen Semenchenko, a militia commander-turned-lawmaker who is also theoretically a Poroshenko ally, said Thursday that he and other volunteer commanders were forming an alternative “coordinating headquarters” to exchange intelligence and battle planning. The group would exist outside the formal structures of the Ukrainian military, an unusual decision that suggested splits in the military command.

Poroshenko’s request for international peacekeepers would depend on finding a peacekeeping force acceptable to both sides, probably ruling out any involvement for European Union, U.S. or Russian soldiers.

A Ukrainian military spokesman said Thursday that more than 90 percent of its forces had been withdrawn from Debaltseve. Reporters who visited the devastated town Thursday said they heard continued shooting at its outskirts, suggesting that some final holdouts may remain there. Rebels were fully in control of the territory.

The trauma hospital in government-held Artemivsk — about 30 miles northwest of Debaltseve — was largely cleared Thursday of the wounded soldiers who were there a day earlier, although the smell of dirt, sweat and blood lingered in the halls.

Doctors and nurses would not say how many soldiers they had treated.

But Yura Sadyha, 29, a soldier who had returned from the front a few days earlier and volunteered to help carry the wounded into the hospital, said that more than 200 soldiers came through it Wednesday for treatment.

“It’s an awful situation, because so many more people were left on the battlefield,” Sadyha said, rubbing his eyes after working at the hospital for 24 hours straight.

Demirjian reported from Artemivsk.