The West yesterday announced a "get tough" policy towards Bosnia's Serbs, the day after the Serb parliament effectively severed links with the rest of the country over the fate of a key strategic town.
Mr Carlos Westendorp, the senior western official in Bosnia, said NATO troops may enforce Friday's decisions to place the Serb-held town, Brcko, under neutral control and to sack Serb President Nikola Poplasen.
"If he doesn't go on his own, local security forces will have to remove him," Mr Westendorp told the Spanish newspaper El Pais. "If they don't do it, international troops will be in charge of it."
His threat, which came the day after the Serb parliament voted to ignore the decision on Brcko, and on Mr Poplasen, and to withdraw Serb officials from the country's institutions, is a focus for genuine concern for the Serbs. An otherwise humdrum little town on the northern border with Croatia, it is the only narrow link between western and eastern parts of Serb territory. In any future war with the Croats and Muslims, its loss would cut Serbian forces in two. The town had a pre-war majority of Croats and Muslims, whom the Serbs have prevented from going back home, and the decision of the US-headed arbitration commission to award it to a neutral government is seen as a way of allowing them to return.
But the decision cuts to the heart of Bosnia's problems. Serb leaders say they do not want to live with Croats and Muslims. The West, fearing the alternative will be war, says they must.
Mr Westendorp's officials said yesterday that Serbia's parliament has acted illegally, and international aid to this impoverished area may be cut unless the Serbs change their minds.
"Poplasen is the ex-president, he is finished," said spokesman Mr James Ferguson." It will be impossible to have financial aid, donor aid, things like that."
Mr Westendorp has the backing of the United States and Britain among Western powers, who link the actions of Serb nationalists in Bosnia with the belligerent tone of Mr Slobodan Milosevic, the Serb president of Yugoslavia, over Kosovo.
"The point to underline is a strong message to Serb hardliners that we are not going to let them set the agenda either in Bosnia or Kosovo," said Mr Charles Hay, spokesman at Britain's Foreign Office.
Yet it is far from clear who will emerge the victor from what is rapidly becoming a test between international will and the resolve of Serb nationalists.
This confrontation was initiated by the nationalists, when last week Mr Poplasen moved to sack his pro-western prime minister, Mr Milorad Dodik. Mr Westendorp saved Mr Dodik by using emergency powers as high representative to sack Mr Poplasen, only to see Mr Dodik feel compelled to resign when the decision of the US-headed arbitration commission to Brcko was announced the same day.
Now the nationalists can afford to sit back and wait for Mr Westendorp's move.
"On the face of it, it looks like a disaster," said Mr Colin Soloway, of the US-funded think tank International Crisis Group based in Sarajevo. "The question is, who is going to back down?"
Mr Westendorp has several options. Aside from sending NATO troops based in Bosnia to occupy the Serb parliament, and garrison Brcko, he can go through with hints to cut aid.
But the "aid weapon" has already been deployed - the Serbs have had millions of pounds of aid withheld because of failures to arrest war crimes suspects, or to allow Croat and Muslim refugees back to Serb territory.
Bosnia's Serb Republic remains mired in poverty, with most aid now channelled to the much richer Croat-Muslim Federation, where some progress on re-integration is being made.
But the result has surprised Western officials. Serbs have continued to back their hardliners and their blunt message that the world is against them.
Mr Radovan Karadzic, their former war-time leader, and now in hiding from NATO which wants to arrest him on charges of genocide, remains a popular cult figure among ordinary Serbs. Ethnic hatred is deeply embedded in the population, particularly in rural areas.
Last autumn Serbs voted for Mr Poplasen, signaling they would rather live poor, in their own state, than better off surrounded by their former enemies.
Diplomats hope moderate Serbs in parliament will assert themselves once the anger about Brcko has died down. "Clearly there's a lot of emotion flying around," said Mr Ferguson. "We're waiting for the dust to settle."