Yesterday, the Bosnian Serb military staff based in Bijeljina warned Ms Plavsic that it would move against her to prevent the Republika Srpska splitting in two.
Ms Plavsic yesterday appeared to have wrested control of the Banja Luka police from officers loyal to Mr Karadzic and the UN has started re-training Bosnian Serb policemen in Banja Luka to create a "non-political" police force as part of efforts to defuse conflict within the Serb community and to consolidate a peaceful, democratic society. But the Bosnian Serb military remains an obstacle.
The Republika Srpska comprises two lobes connected by the narrow Posavina corridor running past Brcko in the north. The political division reflects the geographical: Banja Luka, a large city in the north-west, is one of two main power centres in the Serb "entity" within Bosnia. The other is Pale in the east, the official "capital", a former ski resort outside Sarajevo. Banja Luka is Ms Plavsic's power base, and its politics have traditionally been more moderate, in contrast to Pale, where Momcilo Krajisnik, the Serb representative on the three-man Bosnian presidency, Mr Karadzic and General Ratko Mladic are based.
A civil war between Serbs would probably split the Bosnian Serb republic on those lines, weakening it, inviting the Muslims to push north through the Posavina corridor - which was almost cut during the 1992-95 civil war - making it easier for Muslim and Croat refugees to return home and for Nato troops to seize Mr Karadzic and General Mladic, who are wanted for war crimes.
"If individual actors in the crisis should continue to destabilise and destroy the state, the army of the Serb Republic shall no longer tolerate and warn but shall undertake measures to defend integrity, sovereignty and constitutional order," the Bosnian Serb general staff said in a statement released in Pale. It was clearly aimed at Ms Plavsic, and noted that the military had warned her last month that the international community could exploit the internal dispute to weaken the Bosnian Serb "republic".
Ms Plavsic seems to be winning control of the police, leaving the military as the last bastion of pro-Karadzic forces.
On Wednesday, 350 British and Czech troops swooped to disarm pro-Karadzic police in Banja Luka who were believed to be plotting a coup against Ms Plavsic. The international stabilisation force - S-For - reduced its active presence on the streets of Banja Luka to 250 on Thursday. Yesterday they were hoping to reduce it further although extra troops will remain on patrol until the International Police Task Force has completed investigations into alleged human rights abuses by police.
Serb policemen who want to serve in the new force are being vetted to check they have no criminal record or outstanding allegations of human rights abuses against them. In practice, they are being asked to sign a pledge of loyalty to Ms Plavsic. International officials said many police were responding throughout the region.
"Plavsic has made a gaping hole in the police network and the army has refused to get involved while tacitly supporting Plavsic," a diplomatic source said last night. If the Karadzic faction is putting its faith in the Bosnian Serb military, its position is looking increasingly desperate.