BELGRADE, Yugoslavia (AP) -Russia pushed a peace plan for Yugoslavia yesterday as a chagrined NATO sought to explain how another of its missiles went astray, damaging a house near the capital of Western ally Bulgaria.

The Rev. Jesse Jackson arrived in Belgrade on a mission to win freedom for three U.S. POWs held by Yugoslavia.

NATO, meanwhile, continued its air assault on Yugoslav targets, striking during daylight in Kosovo and at bridges leading into the province. Heavy explosions and intense anti-aircraft fire were reported yesterday afternoon near an oil refinery northwest of Belgrade.

Air raid sirens sounded last night in Novi Sad, Yugoslavia's second-largest city. Serbian television, a frequent target, went off the air last night moments after a strong explosion and anti-aircraft fire was heard in Belgrade.

Yugoslav media said the targets included relay towers for government and private television stations around Belgrade and to the north of the capital.

As the bombings persisted for the 37th day, former Russian Prime Minister Viktor Chernomyrdin launched his latest peace initiative, promoting what Moscow said was a new plan for ending the Kosovo crisis.

While acknowledging "movement" toward a settlement following talks with the Russian envoy, German Chancellor Gerhard Schroeder insisted that Yugoslav President Slobodan Milosevic has to withdraw Serb forces from Kosovo first before the bombing could be suspended.

U.N. Secretary-General Kofi Annan met in Moscow with Russian President Boris Yeltsin, who stressed the need for the United Nations to play a major role.

"The stakes are now very high, not only for the Balkans and Europe, but for the whole world," Yeltsin said.

Bulgarian officials said a NATO AGM-88 HARM missile slammed late Wednesday into a house in a suburb of the capital, Sofia. Konstantin Varbenov was shaving on the top floor of his two-story home when the missile blew away his roof. His wife, child and grandmother, also in the house, were shaken but there were no injuries.

Bulgarian President Petar Stoyanov demanded an explanation.

In Brussels, NATO spokesman Jamie Shea said an alliance jet fired the missile "in self-defense" at Serb anti-aircraft batteries but it "strayed from its target and unintentionally landed in Bulgaria," 30 miles from Yugoslavia's southeastern border.

It was not the first time NATO missiles have gone awry in the Kosovo conflict. On Tuesday, a NATO missile slammed into a civilian neighborhood in a southern Serbian town, killing 20 people.

NATO said the target was a military barracks but the missile apparently veered off course when smoke interfered with its guidance system.

Errant airstrikes on April 12 and 14 left 92 others dead.

NATO officials acknowledge the errors but say only "a tiny fraction" of its 4,500-plus air attacks on Milosevic's war machine have led to "unintended consequences."

The alliance was apologetic about the Sofia accident, with Shea promising to "minimize still further the chance of this happening again."

In Bonn, the first stop on a mission that will also include Rome and Belgrade, Chernomyrdin insisted a halt to the bombing was a precondition for peace talks, something the alliance has repeatedly refused.

"What talks can there be otherwise? It is useless trying to resolve the problem under bombs," Chernomyrdin said.

But Schroeder, who conferred for 90 minutes with the Russian envoy, dampened expectations of an imminent breakthrough. "This is the beginning of a political process, not the end," he said.

Afterward, Vice President Al Gore spoke to Chernomyrdin by phone to reiterate NATO conditions for ending air strikes before the Russian envoy went to Belgrade, a Gore spokesman in Washington said. In addition, Secretary of State Madeleine Albright conferred with Russian Foreign Minister Igor Ivanov on the Balkans situation.

The Russian plan calls for a U.N.-controlled international peacekeeping force in Kosovo.

Yugoslavia's ambassador to Russia, Borislav Milosevic, who is also the Yugoslav leader's brother, said Belgrade would accept a civilian U.N. force with a large Russian component but excluded any NATO participation, Russia's ITAR-Tass news agency reported.

"An international presence in Serbia's Kosovo province is not a problem," the spokesman of Milosevic's Socialist Party, Ivica Dacic, said yesterday. "But only a civilian and unarmed mission under U.N. auspices, with Russia's participation, would be acceptable.

"Those who are bombing Yugoslavia today cannot be a part of any peace mission."

Jackson, who arrived in Zagreb, Croatia, before driving to the Serbian capital, said he hoped freeing the American soldiers could give new impetus to peace efforts, although the White House has demanded their unconditional release. The three were captured March 31 along the Yugoslav-Macedonian border.

"My experience has been whenever captured soldiers are released, it at least creates a window for dialogue," Jackson said. He was accompanied by a delegation of U.S. religious leaders on the trip to Belgrade, where they hoped to meet Milosevic and see the prisoners.

Jackson went to Syria in 1984, where he successfully arranged the release of a U.S. Navy pilot whose jet bomber was shot down by Syrian anti-aircraft over Lebanon. Several months later, Jackson worked out arrangements with Cuba for the release of 48 American and Cuban political prisoners.

Outlining details of yesterday's strikes, NATO's Shea said alliance forces hit an airport near the Montenegrin capital of Podgorica with about 30 missiles in the early hours.

NATO Brig. Gen. Giuseppe Marani said the alliance would have preferred not to strike targets within Montenegro, Serbia's junior partner ruled by a pro-Western leadership, but "Podgorica airfield is becoming an important operating location for the Yugoslav aircraft."

During pre-dawn attacks yesterday, the alliance also struck for the first time against Milosevic's hometown, Pozarevac, 50 miles southeast of Belgrade, the official Tanjug news agency said. Milosevic's Belgrade home was hit last week.

NATO launched the air campaign on March 24 to force Milosevic to accept a Western-dictated peace deal for Kosovo, a province of Yugoslavia's main republic Serbia but with a prewar majority ethnic Albanian population of 2 million.

More than 600,000 ethnic Albanian refugees have fled Kosovo since last month, and hundreds of thousands more are homeless and displaced in the province.

In Macedonia, where 6,000 refugees arrived yesterday, relief workers said a Serb campaign to drive ethnic Albanians from other parts of Serbia is apparently forcing refugees to hike across remote areas where Yugoslav forces have laid mines.

Doctors in the Macedonian capital Skopje treated six land mine victims, including a 2-year-old boy, hospital officials said yesterday.

Another 200 refugees, most from southwestern Kosovo, crossed into Albania yesterday, repeating tales of Serb police or paramilitary units looting and burning their homes.