Sarajevo, Monday,

THE international community today increased the pressure on indicted war criminal Bosnian Serb leader Radovan Karadzic to step down, by threatening to disqualify his party from Bosnian elections.

And prosecutors at the Yugoslavia war crimes tribunal in The Hague urged the major powers to arrest Karadzic and his military commander General Ratko Mladic and hand them over to stand trial for genocide.

The call came as UN investigators began to unearth mass graves of massacre victims, starting with Muslims killed in the Bosnian Serb conquest of Srebrenica a year ago, believed to have been Europe's worst atrocity since the Second World War. The site was today placed under guard and wired off.

Both men remain in office but behave differently. Mladic has kept a low profile and helped to implement the military aspect of the Dayton accord.

In contrast, Karadzic has done much to disrupt the peace process, restricting freedom of movement to preserve his Bosnian Serb republic, and intimidating the opposition ahead of the elections.

International mediator Carl Bildt dared Karadzic to go before The Hague tribunal to try to clear himself of the charges.

``Karadzic should go to The Hague and defend himself, if he had any decency or courage he would go,'' Bildt told reporters in Brussels.

``They are extremely grave charges, one day he will answer them.''

An official organising Bosnia's election threatened to bar the ruling Bosnian Serb party from the September poll if Karadzic, its current chairman, retains any form of office.

US Ambassador Robert Frowick said he would use all his powers as head of the Organisation for Security and Co-operation in Europe (OSCE) mission in Bosnia-Herzegovina to block the Serb Democratic Union (SDS) from the September 14 elections.

``It just isn't right to continue with Mr Karadzic, an indicted war criminal, as its head and we are faced with a defiance that has increased over the past week or so,'' he told the OSCE's fifth parliamentary session in Stockholm.

The Dayton peace agreement, signed last December to end the 43-month war in Bosnia, banned indicted war criminals from holding official positions.

``Karadzic epitomises the over-riding problems of extreme nationalism that brought on the war in the first place and he has pushed against the tide of the peace process since before the ink was dry,'' said Frowick.

He added: ``I frankly have not seen enough resolve by the international community.

``It seems appropriate to me for a decision to be made that would let Ifor (the Nato-led peacekeeping force) move in to apprehend these people and bring them to trial.''

Tonight, however, although the White House supported arrest warrants against Karadzic and Mladic, it gave no indication that its troops would act to enforce them.

``If the war crimes tribunal believes it's useful to issue a warrant, the United States would have to be in a position to support that,'' said State Department spokesman Nicholas Burns.

``How that occurs, how that is turned into reality is another question altogether because, as you know, Ifor has not changed its rules of engagement on indicted war criminals.''

Ifor, with 60,000 troops, including 20,000 Americans, has refused to actively seek out either suspect, saying they would arrest them only if soldiers encountered them.

Instead Burns emphasised US backing for Frowick's plan to disqualify Karadzic's party from the Bosnian elections as long as he remains its leader.-Reuter.