The negotiators, meeting in Minsk, Belarus, said they would reconvene on Monday to discuss the mechanics to carry out the agreement.

Mr. Poroshenko lauded the agreement in a statement posted on the presidential website, paying tribute in his announcement to the fact that Mr. Putin called for a cease-fire with a seven-point plan released Wednesday. Both men said before Friday that they expected an agreement.

A spectrum of politicians, civil society activists, diplomats and other analysts welcomed the proposal but expressed serious doubts that it could hold given the wide rift between Kiev and the restive eastern regions.

“I am pleased; it is impossible to solve this conflict by military means,” said Georgiy Kasyanov, a civil society activist and historian who supported the antigovernment protests that erupted in central Kiev last November and eventually led to the overthrow of the government and the conflict. “People are tired and suffer from psychological depression; we have all been living in a state of shock since November.”

But he, like many, recognized the hurdles ahead. The majority of Ukrainians want peace, he said, but some will be angry about any compromise with the separatist fighters the government has condemned as terrorists for months. In addition, neither side exerts perfect control over the range of fighters in the Donbass region. It will be hard to rein them all in, and any spark could easily reignite the fighting.

The goals of the separatists have never been clear, nor whether they agree even among themselves. “We are planning to continue the course toward secession,” said Igor Plotnitskiy, the prime minister of the self-declared Luhansk People’s Republic, according to the RIA Novosti news service. “The cease-fire is a necessary measure. There is a lot of work ahead of us.”