Hundreds of Bosnian Serbs pelted US peacekeeping troops with stones yesterday in response to the ousting of hardliners from a local police station in a continuing power struggle between Serb factions.
The Americans arrived in Brcko in north-eastern Bosnia in armoured personnel carriers in the dead of night but were forced to retreat after an air raid siren brought angry crowds with wood and metal bars on to the streets.
A western official said the soldiers had already succeeded in their mission of replacing hardline policemen loyal to the indicted war criminal, Dr Radovan Karadzic, with officers supporting Bosnian Serb President Biljana Plavsic.
"Everything has changed. There's going to be a new police force here," the official said.
NATO, which commands the 35,000-strong Stabilisation Force (SFOR) peacekeeping troops, said it was conducting security operations to deter the outbreak of violence in the Serb part of Bosnia.
"These actions have been taken due to the potential for confrontation in the Republika Srpska between police forces in support of the government of President Biljana Plavsic and factions based in Pale," a statement asserted.
Ms Plavsic, with strong backing from the West, is locked in an increasingly high-stakes struggle with supporters of Dr Karadzic, the Bosnian Serbs' leader during the 43-month Bosnian civil war, for control of state institutions, including police, state television and the army.
The West, particularly the United States, has put intense pressure on President Slobodan Milosevic of Yugoslavia, the Bosnian Serbs' chief patron, to intercede on Ms Plavsic's side. Mr Milosevic's aircraft has been cleared to land in Banja Luka, airport officials said yesterday.
The Brcko incident was the most serious and violent in weeks of an escalating struggle for power. The town lies in a narrow corridor of Serb-held territory, near the region controlled by Dr Karadzic's hardliners.
All went smoothly for the US troops until an hour after their arrival and the air raid siren sounded. Hundreds of people, cursing and shouting "get out of here" and "leave", poured into the streets.
Elderly women at the front of the crowd battered the gun turrets of the armoured vehicles while other people threw stones, forcing the troops to retreat from positions in front of the police station and drive back across a bridge.
Two US peacekeeping troops were hurt by the stone-throwing, club-wielding crowd after they ousted Bosnian Serb hardliners from control of the police station.
The White House said the US will not tolerate such attacks: "It's important that all of the parties there understand that they should not challenge SFOR, and that we will hold the leadership responsible for keeping their people under control.
"We're continuing to work with both sides and we won't tolerate either side inciting . . . violence against the SFOR troops," White House spokesman Mr Joe Lockhart told reporters on the island of Martha's Vineyard, Massachusetts, where President Clinton is holidaying.
In Brcko, angry groups of young men roamed the streets afterwards.
The western official, who asked not to be identified, said police loyal to Ms Plavsic were asserting their authority and had put a halt to the sirens which wailed for several hours.
At another hardline-controlled town, Bijeljina, reporters said local residents had blocked the town centre to stop SFOR troops from taking over the police station and a transmitter.
And in Doboj, north of Sarajevo, residents attacked NATO tanks with wooden clubs.
"We expect this type of resistance to continue for the next five to seven days and to taper off once they realise that we are serious, that we are not backing off," a NATO officer said, on condition of anonymity.
The NATO statement said some factions were armed with "unauthorised long-barrelled rifles" and that the peacekeepers had increased their reconnaissance patrols and stationed units at strategic locations.