(CNN) German Chancellor Angela Merkel said Saturday that prospects for peace in Ukraine are "uncertain" following talks with Russian President Vladimir Putin.

Merkel and French President Francois Hollande met with Putin in Moscow on Friday.

On Saturday, at the annual Munich Security Conference , she said it is uncertain whether their talks were successful, but it was worth trying. She defended borders in Europe as "inviolable."

Russia has shown disrespect for peace and territorial integrity, she said, and Moscow's actions in Ukraine stand in stark contrast to their commitments.

Changing borders by force is out of line with peace and security, and risks escalation, she said.

The French, German and Russian leaders met to begin drawing up a new proposal to end the bitter conflict in eastern Ukraine. The peace talks lasted into early Saturday. The parties will engage in further talks by phone on Sunday, the Kremlin said.

"We want to shape security with Russia, not against it," Merkel said.

U.S. Vice President Joe Biden, addressing the conference after Merkel, said it was time for Russia not to just agree to peace -- referring to a September ceasefire between Ukraine and pro-Russian separatists that was agreed in Minsk, Belarus -- but to act on it.

"Too many times, President Putin has promised peace and delivered tanks, troops and weapons," Biden said, restating Western assertions about Russia's involvement in the conflict.

"We believe we should attempt an honorable peace. We also believe the Ukrainian people have the right to defend themselves," Biden said, drawing robust applause.

Russian Foreign Minister Sergey Lavrov told the conference that his country "will be committed to peace."

"We are against combat. We would like to see a withdrawal of heavy weapons," Lavrov said. He called for "a direct negotiation" between Ukrainian government leaders and separatist leaders in Donetsk "within the framework of territorial integrity."

Lavrov said talks will continue, adding, "We believe that there are good grounds for optimism to issue recommendations for conflict resolution."

The new diplomatic push comes as a worsening conflict in eastern Ukraine is taking an increasingly heavy toll on civilians.

Merkel made clear that she would not do a deal with Russia that bypasses Ukraine's leadership, saying she "will not decide anything over the heads of anyone." The solution must be in line with the Minsk agreement, she said.

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Russia, Ukraine and separatist leaders signed that pact, but continued fighting has left it in shreds. It's not yet clear how the new proposal differs from the Minsk agreement.

Hollande said Thursday that the joint proposal for new negotiations would be "based upon the territorial integrity of Ukraine ."

The pair hope the proposal will be acceptable to all parties in the conflict, he said. But he said that "the option of negotiation, of diplomacy, cannot be extended indefinitely."

Merkel is scheduled to meet with U.S. President Barack Obama in Washington on Monday to discuss, among other topics, Ukraine.

Western leaders and Kiev accuse Russia of fostering the conflict by providing weapons and training to the pro-Russian separatists battling Ukrainian forces in the Donetsk and Luhansk regions, as well as sending regular Russian troops over the border to fight. Moscow denies the allegations.