SARAJEVO, Bosnia-Herzegovina (AP) _ Bosnian Serb soldiers kidnapped three Ukrainian peacekeepers from an observation post near Gorazde, bringing to 377 the number of U.N. soldiers held hostage, officials said today.

Official sources in the Bosnian Serb stronghold of Pale said 120 peacekeepers would be released later today. The sources spoke only on condition of anonymity. No further information was immediately available.

Bosnian Serb leader Radovan Karadzic warned Thursday against trying to rescue the U.N. hostages, scattered throughout Serb-held territory, saying such attempts would lead to slaughter. He said the hostages won't be released unless NATO pledges not to launch any more airstrikes on Bosnian Serb territory.

The three Ukrainian peacekeepers were taken sometime during the night Thursday from their observation post near Gorazde, southeast of Sarajevo, after having been surrounded by Serbs for several days, said Lt. Col. Gary Coward, a U.N. military spokesman.

The U.N. soldiers ``were buying time trying to get away'' from their checkpoint, but the U.N. command in Gorazde was informed this morning that the three had been seized, Coward said.

The latest detentions brought to 377 the number of U.N. peacekeepers held hostage or blockaded in Bosnia, Coward said.

``We demand the unconditional release of the hostages,'' said another U.N. spokesman, Alexander Ivanko.

A U.N. civilian official, a Swedish national, was released after being held briefly by Serb rebels in northern Bosnia, the Swedish Foreign Ministry said today.

Goran Stigmer, a 46-year-old U.N. Civil Affairs officer in Banja Luka, was handed over to U.N. authorities in neighboring Serb-held Croatia, the ministry said. U.N. officials said his detention did not appear to be directly linked to the other U.N. hostage-taking.

Karadzic repeated demands Thursday for the complete demilitarization of Sarajevo and other government-held enclaves and a halt to clandestine arms shipments to the Bosnian army.

But a world angered by the detentions rejected any deal with the Serbs.

Western allies instead flexed their military muscle, pinning their hopes on a new rapid-deployment force that could either reinforce the U.N. mission in Bosnia _ or help it leave.

President Clinton has said he could make U.S. ground troops available to help move U.N. peacekeepers to safer posts in former Yugoslavia.

Formation of the new force is expected to dominate a meeting of European defense chiefs and military commanders in Paris this weekend, and a NATO defense ministers' session next week.

Although isolated and facing an improving government army, Karadzic indicated he believes his men still have the edge and are risking little if the United Nations does pull out.

``If the U.N. troops want to leave, they don't need NATO, they can go through our territory peacefully under condition that they take their weaponry with them,'' Karadzic said Thursday evening on television.

``If they want to stay, they have to be impartial, but if the mandate is changed without our consent and if we are not satisfied with it, there will be more conflicts with the U.N.,'' he declared.

The Bosnian Serbs detained the peacekeepers last week after NATO launched airstrikes to punish the Serbs for refusing to turn over some heavy weapons in compliance with last year's agreement to remove such weapons from a 12.5-mile radius around Sarajevo.

The detentions dramatically underlined the weakness of the U.N. mission and led to new calls for military action by the West.

The Bosnian Serbs' ability to squeeze the government was evident in fresh warnings Thursday from aid officials that Sarajevo is again running short of food.

The humanitarian airlift into Sarajevo has not operated for almost two months. Although it is summer, and almost every Sarajevan has home-grown vegetables, there is only two days' supply of wheat flour in the city. The Serbs have prevented the transport of 10 more days' supply from the airport to the city, U.N. aid officials said.

Fighting flared in the east and northeast of Bosnia on Thursday, and shells again hit Tuzla, the government stronghold in the north where a single shell killed 70 people last week after NATO jets bombed a Serb ammunition dump.

Western allies dismissed Serb offers of international talks on the hostages, while trying to persuade President Slobodan Milosevic of Serbia to further isolate the Bosnian Serbs by recognizing Bosnia.

Milosevic supplied weapons to the Bosnian Serbs, spurring them to start fighting after Bosnian Muslims and Croats voted to secede from Yugoslavia in 1992.

But international sanctions have shattered Serbia's economy and Milosevic has broken with Karadzic. If Serbia recognizes Bosnia in exchange for the lifting of sanctions, Karadzic's position would be further weakened.

On Thursday, U.S. envoy Robert Frasure offered Milosevic economic ties with the West in exchange for giving up his ambitions to unite Serb-held territory in Croatia and Bosnia with Serbia itself.

Milosevic rejected the offer, but U.S. officials said he disapproved of the hostage-taking by Karadzic's forces.