DNIPROPETROVSK, Ukraine - Pro-Russian separatists rejected a call Wednesday to disarm during a cease-fire that Ukraine was preparing to start unilaterally within days.

Ukrainian President Petro Poroshenko said the truce would be the first step of a 14-point plan to end the violence that has engulfed the east of the country for months. Acting Defense Minister Mykhailo Koval gave a timetable of days, while Poroshenko said only that the cease-fire would get underway "shortly."

The peace proposal includes sealing the border with Russia, disarming the insurgents, offering amnesty to those who did not commit serious crimes, and providing safe passage to rebels willing to leave the country. The president also promised to pursue constitutional amendments that would decentralize power and grant regional governments more say.

"I can say that the cease-fire time will be pretty short," Poroshenko told reporters after a speech before graduates of the National Defense University. "We expect that disarmament of military groups and restoration of order will take place right after it."

But separatists, who have been battling government forces for almost three months, promptly rejected the offer from Poroshenko, whom they said they did not trust.

"This proposal by Poroshenko to lay down our arms is simply a tactical ploy," said Myroslav Rudenko, a spokesman for the separatists' self-proclaimed Donetsk People's Republic, according to the Russian Interfax news agency. "If people fall for it, there will be a new mopping-up operation. We will not put our weapons away."

In Moscow, Denis Pushilin, a Donetsk rebel leader, called Poroshenko's gesture a "pointless proposal."

Russian Foreign Minister Sergei Lavrov expressed skepticism at the proposal, saying Russia expected a full-scale, permanent cease-fire. A temporary truce, in which those of pro-Russian sentiment leave the country, he said, "is close to ethnic cleansing."

This is the third time in less than two weeks in office that Poroshenko has publicly signaled that he would declare a cease-fire. He proposed a truce in his inaugural address June 7, but rebels rebuffed the call. As recently as Monday, he ordered Ukrainian defense forces to seal the porous border with Russia as a prelude to a cease-fire.

Poroshenko made no mention Wednesday about what might happen if the rebels refused to disarm and surrender, although Ukraine's stand seemed to carry an implicit threat that the war could intensify.

Adding to the sense that more fighting could be on the horizon before there is peace, Ukrainian officials said Russia was continuing a military buildup close to the border. Meanwhile, fighting continued in eastern Ukraine, where officials said that 15 soldiers had died in the Luhansk region Tuesday and that 13 were unaccounted for.