On Saturday, the United States special envoy, Robert Gelbard, accused hard-line supporters of wartime leader Radovan Karadzic of instigating the violence, and criticised them for using women and children as shields for rock-throwing demonstrators.
Mr Gelbard, on a one-day visit to shore up the crumbling Dayton peace accords and stem mounting violence that has included attacks on US soldiers, gave measured support to the more moderate Bosnian Serb leader, Biljana Plavsic, but heaped scorn on her hardline rivals. He said the backers of the indicted war criminal Radovan Karadzic had impoverished the Bosnian Serb people, whose economy was wrecked during the 43-month-long Bosnian civil war.
"I warned him in the most serious terms that there is a need right now to change his behaviour," Mr Gelbard said after he met Momcilo Krajisnik, a top Karadzic aide. "The consequences will be the most serious imaginable," he added.
Mr Krajisnik hit back at Mr Gelbard. "We took Gelbard's message very seriously, but we don't accept threats," he said.
The Bosnian Serbs' embattled President Plavsic met the US administrator of Brcko, where intra-Serb tensions sparked attacks against US peacekeeping troops three days ago. After speaking with the administrator, Robert Farrand, for two hours, Mrs Plavsic condemned her hard-line rivals for "putting women and children in the front line ... which is beyond every moral norm".
Mrs Plavsic controls the western section of Serbian territory in Bosnia from her base in Banja Luka, while Mr Karadzic controls the east from Pale, near the capital, Sarajevo. The peace force and other international representatives in Bosnia have sided increasingly with Mrs Plavsic.
Clashes erupted in Brcko after US soldiers serving with the Nato peace mission moved to maintain order after learning that Mrs Plavsic's forces were planning to seize police stations and media outlets controlled by her rivals. Mr Farrand criticised local radio in Brcko for instigating Thursday's violence.
The North Atlantic Council, Nato's policymaking body, said on Saturday that Nato-led troops in Bosnia "would not tolerate the use of force or intimidation" and promised to shut down any media inciting violence. The council met in special session late on Saturday to consider the developing situation in the Serb part of Bosnia-Herzegovinia.
The Nato Secretary-General Javier Solana said that allied peacekeeping troops would use force, if needed, to shut down Bosnian Serb media outlets that urge violence against peacekeepers.
President Plavsic warned that the hardliners would face punishment when the power struggle in Bosnian Serb territory was over. "Their biggest punishment would be their conscience, if they had one," she said during a television programme on Saturday night. "Since they do not have one, they will be punished once all this over."
The West, together with Mrs Plavsic, have been gradually wresting power from the hardliners in the west of the republic, including putting Plavsic loyalists in charge of police stations. They also have been taking control of the state-run television network, which previously broadcast only news programmes put together by the hardline-run studios in Pale.