Bosnia's top international envoy, Paddy Ashdown, has sacked nine Bosnian Serb officials suspected of aiding fugitives from the Hague war crimes court.
International troops have been leading the hunt for suspects
The US also announced a visa ban on top Bosnian Serb politicians and a freeze of a leading political party's assets.
Mr Ashdown, whose sweeping powers date to the 1995 Dayton Agreement, dismissed six policemen and three others accused of impeding the hunt for suspects.
UN lawyers accuse Bosnian Serb leaders of shielding war crimes suspects.
Since the establishment of the international war crimes court in The Hague, the Bosnian Serb republic has not arrested a single suspect believed to be hiding on its territory.
At the top of the court's list of suspects are Radovan Karadzic and Ratko Mladic, leaders wanted for the genocidal campaign of ethnic cleansing that swept Bosnia during the war in the 1990s.
Mr Ashdown said on Thursday that he believed Mr Mladic had recently revisited his army's old base in the Bosnian Serb republic for a celebratory gathering.
"While the authorities in Banja Luka were telling anyone who would listen of their efforts to apprehend war crimes suspects, members of their own army sat in their own military base celebrating... with Ratko Mladic," Mr Ashdown said.
Speaking alongside Mr Ashdown at a press conference in Sarajevo, US ambassador to Bosnia, Douglas McElhaney, said the leaders of two major Bosnian Serb political parties - the Party for Democratic Progress and the Serb Democratic Party - would be forbidden from visiting the US.
Mr McElhaney said the financial assets of the party in the US would also be frozen.
The Treasury Department in Washington announced a further freeze on the assets of two firms, Zdravo and Komoto, suspected of collaborating with war crimes suspects.