Refugees from eastern Ukraine arrived in Kiev after being driven out by constant shelling, as the U.S. denies a split with Europe over their Russia policy. (Reuters)

The viability of a joint French and German proposal to halt fighting in eastern Ukraine faced significant hurdles Saturday as European and American officials attending a security conference demanded that Russia withdraw its troops while Russian officials blamed the United States for the escalating violence.

The laborious attempts to forge a deal highlighted what was being portrayed in European capitals as a last-ditch effort to prevent a sharp escalation of hostilities in a conflict raging for months on the eastern fringes of Europe. The new cease-fire proposal, being pushed by German Chancellor Angela Merkel and French President François Hollande, follows the outlines of an agreement reached in September that ultimately crumbled.

Without a speedy resolution, the conflict between Russian-backed separatists in eastern Ukraine and the pro-Western government in Kiev appears poised to spread and deepen. According to State Department officials familiar with some details of the new plan, one sticking point is the demarcation line between forces if a cease-fire takes effect. The Ukrainians want it to be the same as agreed to last fall. The pro-Russian rebels want it to reflect the changed realities caused by their latest offensive, said the officials who spoke on the condition of anonymity because the talks are at a sensitive stage.

The crisis in eastern Ukraine, where government forces are besieged by separatists widely said to be supported and armed by Moscow, is dominating the Munich Security Conference, an annual event drawing national security officials, analysts and policymakers from around the world. The conference, which ends Sunday, is fueled with urgency born of fear that a broader expansion of the war is near.

Merkel and Hollande have expended serious political capital launching a bid for a new cease-fire in recent days. The pair flew to Kiev and then Moscow, with Merkel due for talks at the White House on Monday. The leaders of Germany, France, Ukraine and Russia are additionally scheduled to hold a conference call Sunday to discuss the peace initiative, which Hollande characterized as a last-ditch effort. Those nations’ leaders, the Associated Press reported early Sunday, plan a summit Wednesday in Minsk, Belarus, with the hope of creating measures to reinvigorate a peace plan put forth in September.

Thousands of Ukrainian civilians are trapped between the battle lines in the renewed fighting.

“Because if we are not able to reach, not a compromise but a durable peace accord, we perfectly know the scenario,” he said in an interview with French 2 television. “It has one name. It is called war.”

Merkel on Saturday offered a tempered assessment of the chances for a deal and cautioned that an agreement might not be upheld by the Russians even if one were struck. But trying, she said, was better than not.

Vice President Biden and NATO Secretary General Jens Stoltenberg also expressed cautious support for a face-saving compromise that would have Russia pull back thousands of its soldiers and seal the border. Biden also was openly skeptical that Russia would stick to any deal. “Too many times, President Putin has promised peace and delivered tanks, troops and weapons,” he said.

Few details are known of the proposal Merkel and Hollande laid out Friday to Russian President Vladimir Putin. In his television interview, Hollande said it would open up a buffer zone and create greater autonomy for disaffected regions of eastern Ukraine, where separatists last year declared two “people’s republics” around the cities of Donetsk and Luhansk. Last year’s cease-fire agreement also included a narrower demilitarized zone with little lasting effect. The government in Kiev already has promised to give the east a measure of autonomy.

A bipartisan congressional delegation to the conference of nine Republicans and six Democrats — all of whom favor the United States sending lethal weapons to Ukraine — met with Ukrainian President Petro Poroshenko, who played down the prospects for peace.

“It’s safe to say he is not overly optimistic about these negotiations,” said Sen. John McCain (R-Ariz.), who led the group.

Sen. Bob Corker (R-Tenn.), the new chairman of the Senate Foreign Relations Committee, noted that Ukraine is facing an economic crisis as well. “Ukraine is on the brink,” he told reporters. “We need to help it with significant financial support, sanctions and arms.”

The conference underscored the wide gulf separating competing narratives offered up by Russia and virtually everybody else.

Officially, Russia continues to deny sending its soldiers into Ukrainian territory, although evidence from Western satellites and eyewitnesses suggests otherwise. In a particularly dramatic display that he said disproves Russia’s claims, Poroshenko held aloft several red passports that he said came from Russian soldiers fighting on Ukrainian soil. He plaintively asked how much “evidence does the world still need to recognize the obvious fact, there is foreign military equipment, Russian military coaches and regular troops” operating in Ukraine.

Russian Foreign Minister Sergei Lavrov in turn accused the West of supporting a government in Kiev that he said came to power via a “coup d’etat” as well as anti-Russian and xenophobic paramilitaries.

“Through every step, as the crisis has developed, our American colleagues and the [European Union] under their influence have tried to escalate the situation,” Lavrov said. But few in the audience bought his claims that Russia is not fostering violence in eastern Ukraine. They peppered him with skeptical questions, and Lavrov at one point looked wearily at his wristwatch.

Fear of Moscow’s ambitions was most palpable at the conference among officials from Russia’s smaller neighbors. Asked why, Lithuanian President Dalia Grybauskaite, answered succinctly: “After Ukraine, we will be next.”

Michael Birnbaum in Brussels contributed to this report.