BELGRADE, Yugoslavia (AP) _ NATO-led forces stepped in Sunday to try to ensure that a standoff between backers and opponents of Bosnian Serb President Biljana Plavsic would not erupt into violence.

The peacekeeping force was sent to Bosnia in 1995 to separate Muslims, Serbs and Croats after a 3 1/2-year war. However, bitter disputes have emerged among Serb factions that threaten to split their half of Bosnia in two.

Plavsic is in a protracted dispute with officials in Pale, a Serb headquarters just outside Sarajevo. She accuses them of corruption and continued loyalty to strongman Radovan Karadzic, who is accused of overseeing wartime atrocities that included the deaths of thousands of Muslims.

International officials say tensions in Bosnia cannot ease without the capture of such war crimes suspects.

A London newspaper reported Sunday that a combined U.S., British and French commando force has been deployed in Bosnia to capture Karadzic. Citing unidentified military sources, The Sunday Times said the group carried out a night exercise Wednesday in mountains north of Pale in what was widely seen as a dress rehearsal for his capture.

Meanwhile in Banja Luka, Plavsic's headquarters in northwest Bosnia, journalists said police loyal to her marched into the town's main police station early Sunday and seized transcripts of what were reported to be her telephone calls, apparently bugged by opponents.

The police were led by Maj. Dragan Lukac, the chief of security for Plavsic.

Police loyal to Plavsic were surrounded by about 150 policemen armed with pistols, and the NATO-led peace force surrounded both of them with a force that included armored vehicles, the journalists said.

``The interest of international organizations is in ensuring that the matter is resolved peacefully,'' said NATO spokesman Maj. John Blakeley in Sarajevo. ``In no case will violence be tolerated.''

He said the peace force was reestablishing control in the area.

NATO officials who spoke on condition of anonymity said they had turned down a request from Karadzic ally Momcilo Krajisnik in Pale to send another unit of well-equipped special police to Banja Luka.

In any case, the dispute illustrated the worsening divisions among Serbs.

The Bosnian Serb Constitutional Court on Friday said Plavsic did not have the authority to dissolve parliament and call new elections. But a top Plavsic aide said Sunday that the president will ignore the ruling and go ahead with new elections.

Milos Prica said the elections would be held Oct. 12, the independent BETA news agency reported.

It remains unclear how Plavsic would organize campaigning, voter registration and balloting, because some of the existing state bodies, including much of the police and army, may decide to respect the court ruling.

However, if she goes ahead, it will certainly deepen divisions among Bosnian Serbs, both politically and geographically.

It would be virtually impossible for Plavsic to organize elections in Serb-held sections of eastern Bosnia, which Karadzic supporters dominate. However, she may be able to hold them in the western part.

If she does, the Serb republic that makes up 49 percent of Bosnia would likely no longer have a common assembly or government institutions.

Plavsic was Bosnian Serb vice president, serving under Karadzic, during the war, and is a strong nationalist in her own right.

However, she broke with Karadzic and his deputies, whom she accuses of enriching themselves through corruption. Western powers and peace mediators consider her more cooperative in their efforts to implement the Dayton peace agreement and bring war crime suspects to trial.