KIEV, Ukraine (AP) -- The new president of Ukraine promised on Wednesday that government troops would soon stop firing on pro-Russian armed separatists, offering a chance to end the fighting that has killed hundreds and wracked the industrial east.
In another concession to Moscow, Petro Poroshenko replaced his foreign minister, who had outraged Russians by using an obscenity to describe President Vladimir Putin.
An end to the two months of fighting and a promised safe exit for rebels would allow Putin to say that Russia has fulfilled its goal of protecting Russian speakers in eastern Ukraine, while Poroshenko can claim victory over the rebellion.
The Ukrainian president discussed his plan for a unilateral cease-fire in a phone call with Putin late Tuesday, their offices said, and Poroshenko also spoke with German Chancellor Angela Merkel.
Russia's foreign minister cautiously welcomed the move, but voiced concern that it could be a ruse. One key question is whether Moscow is willing and able to persuade the pro-Russia insurgents to accept Poroshenko's plan.
Rebel leaders have remained defiant, but in a sign of behind-the-scenes maneuvering, some of them visited Moscow this week to meet with senior officials and lawmakers.
The two sides managed to arrange a brief truce Wednesday evening in the eastern town of Karlivka to allow pro-Russian forces to hand over the bodies of 49 Ukrainian troops who died when the separatists shot down a transport plane bound for the airport in Luhansk last weekend.
But after the truck carrying the remains had passed to the Ukrainian side, both sides fell back to their respective positions. A pro-Russian fighter, whose face was covered with a bandanna and identified himself only by his nom-de-guerre, Sova, said the cease-fire was over. "The war will go on until we win," he said.
U.N. Assistant Secretary-General for Human Rights Ivan Simonovic called Poroshenko's cease-fire announcement "a timely initiative." But he stressed that it was "a real challenge" because U.N. human rights monitors in eastern Ukraine believe there are at least three distinct armed groups that don't fully coordinate.
"This may represent a problem because some of them might be adhering to cease-fires, some not," Simonovic told the International Peace Institute in New York.
If successful, the plan could help ease the worst crisis between Russia and the West since the Cold War, a situation triggered by Moscow's annexation of Crimea in March following the ouster of Ukraine's pro-Russia president.
Poroshenko didn't say when the cease-fire could be declared, but the defense minister, Mykhailo Koval, was quoted as saying it could begin "within days."
"The plan will begin with my order for a unilateral cease-fire," Poroshenko told reporters in Kiev. "I can say that the period of the cease-fire will be rather short. We anticipate that immediately after this the disarming of the illegal military formations will take place."
He said those separatists who lay down their weapons and haven't committed grave crimes would be granted amnesty and a corridor to leave the country if they chose to do so.
Putin has welcomed Poroshenko's peace initiative in an apparent hope that de-escalating tensions with the West would help Russia avoid another round of crippling economic sanctions. Still, embracing the plan would require a delicate balancing act for the Kremlin, which is facing rising demands from Russian nationalists to send troops into Ukraine.
Poroshenko said a cease-fire should follow securing the border with Russia, and Ukrainian officials said Wednesday they were completing the effort. Despite their optimistic statements, sealing the roughly 2,000-kilometer (1,200-mile) border could be a challenging task for the nation's ill-equipped and badly organized armed forces.
Russia has denied Ukrainian and Western claims that it has fomented the insurgency by sending troops and weapons, insisting that Russian citizens among the rebels are volunteers.
Poroshenko made repeated promises to restore peace before and after winning May's election, but Wednesday was the first time he said government forces would be the first to halt hostilities, which has been Russia's main demand.
Denis Pushilin, an insurgent leader in Donetsk, told Russian independent Dozhd television that Poroshenko's latest offer was "senseless."
"They cease fire, we lay down weapons, and then they will capture us weaponless," he said.
Russia's foreign minister, Sergey Lavrov, speaking in Baku, Azerbaijan, said any cease-fire should be "comprehensive" not temporary. He said if it was followed by negotiations "then it could be the step President Poroshenko has promised and which in general we were all waiting for."
U.S. Treasury Secretary Jacob Lew also expressed backing for the plan during a stop in Jerusalem.