After 15 hours of talks in the Belarusian capital, Putin said agreements had been signed, one declaring the cease-fire, the other to implement it. Meanwhile, both rebels and government troops reported fighting across eastern Ukraine, though both are now to have said to have agreed to sign the deal.
Fighting has already killed more than 5,000 people, and Washington is now openly talking of arming Ukraine to defend itself from "Russian aggression", raising the prospect of a proxy war in the heart of Europe between Cold War foes.
A surge in fighting in the 24 hours before the summit, including a rocket attack that killed 17 people in government-held territory on Tuesday, could be intended to force Ukraine to accept a deal recognising the rebel advance.
The summit was being held in neighbouring Belarus under a Franco-German proposal to try to halt the fighting. Chancellor Angela Merkel and President Francois Hollande began talks with Ukraine's Petro Poroshenko and Russia's Vladimir Putin.
French President Francois Hollande said on Thursday that pro-Russian separatists had signed an agreement to end the fighting in eastern Ukraine.
Speaking to journalists, Hollande also said German Chancellor Angela Merkel, Ukrainian President Petro Poroshenko and himself would ask the European Union to support the deal at a summit later in the day.
The leaders were planning to sign a joint declaration supporting Ukraine's territorial integrity and sovereignty, a Ukrainian delegation source said.
A source said a separate document would be prepared by a "contact group" of Russia, Ukraine and the Organization for Security and Cooperation in Europe affirming commitment to a ceasefire plan drawn up in Minsk last September and also signed by separatist leaders.
Earlier, Ukrainian President Petro Poroshenko said there is "no good news yet" from the marathon four-way peace summit in Minsk, saying that Russia was imposing "unacceptable" conditions.
"Unfortunately there's no good news yet," Poroshenko said of the talks involving the leaders of Russia, Ukraine, France and German. "There are conditions that I consider unacceptable," he said, declining to elaborate. "The (negotiations) process is ongoing."
Russia has launched military exercises in 12 regions, involving more than 30 missile regiments, RIA news agency reported on Thursday, citing a Defence Ministry official.
Participants at international peace talks said Thursday that pro-Russian separatists were refusing to sign an agreement unless Kiev agreed to withdraw its troops from the town of Debeltseve.
"No agreement yet. The pro-Russian separatists do not want to sign. They demand the retreat of the Ukrainian army from Debaltseve," said one of the sources at talks between the leaders of Ukraine, Russia, France and Germany in Minsk.
Pro-Moscow forces in eastern Ukraine have tightened the pressure on Kiev by launching some of the war's worst fighting near the railway town of Debaltseve.
Associted Press and Reuters contributed to this report