Ms Plavsic has been struggling to maintain her authority over rivals still loyal to the indicted war criminal and ex-president, Radovan Karadzic. Yesterday's operation succeeded, and at noon she made a triumphant visit to the main police station where she was cheered by several hundred onlookers.
The dramatic action by international peace-keepers was a result of "mutual agreement" with Ms Plavsic, whom they met late on Tuesday, and clearly designed to avert a coup against her. It suggests that a move to seize Mr Karadzic and his "number two", General Ratko Mladic, may be imminent.
At about 6.30am, 350 British and Czech soldiers from the Nato-led multinational stabilisation force - S-For - in 50 vehicles sealed off the Banja Luka police headquarters, the police academy, a special police barracks and three police stations, while the US Apaches hovered overhead. Some of the Bosnian Serbs refused to leave and vowed to "fight to the death".
Five minutes before S-For's ultimatum expired, they came out with their hands up. Officers from the International Police Task Force entered the police stations and found large numbers of unauthorised weapons including machine-guns, rocket launchers and mines, the force's deputy commander, Werner Schum, said. S-For had to bring in three trucks to take 2,500 weapons away.
"S-For met no resistance. S-For is in control. We have deployed sufficient resources to meet any anticipated requirements", its spokesman, Major John Blakeley, said in Sarajevo.
Banja Luka - the second city of the Bosnian Serb mini-state - is also the headquarters of the British-controlled sector. On Sunday, a special police unit loyal to Ms Plavsic raided the main police station after evidence emerged that the police were backing Ms Plavsic's rivals and bugging her telephones with a view to arresting her.
S-For disarmed the police - but that left Ms Plavsic virtually defenceless as about 100 pro-Karadzic police moved into Banja Luka putting her in what international officials described as a "critical situation".