In another day of ethnic violence, Serbs attacked Croat-owned cars on Saturday near Plehane, a Serb-held town in northern Bosnia, where Croats planned to attend Mass.
The incident followed rioting a day earlier in the northwestern town of Drvar, where 15-hundred ethnic Croats burned buildings and stoned and overturned U-N vehicles.
The Croats were angry over an attack on Thursday by Bosnian Serbs on the Croatian Roman Catholic Cardinal, Vinko Puljic.
The latest outpouring of ethnic hostilities in the troubled town of Drvar left 19 people injured, including four U-N officers and the Serb mayor.
The office of the U-N refugee agency, which is overseeing the return of Serbs to the Croat-dominated town, was among buildings burned to the ground.
Officials said NATO peacekeeping troops had to fire warning shots to break up the riot by 15-hundred Bosnian Croats.
The rampage was triggered by Thursday's attack by Bosnian Serbs on a Roman Catholic cardinal, in Serb-controlled Derventa, 130 kilometres (80 miles) east of Drvar.
Vinko Puljic and hundreds of other Croat Catholics had travelled to Derventa to celebrate Mass in a church where Croats had worshipped before the Bosnian war.
Bosnian Serbs threw stones at their buses, then surrounded the church, trapping the Croats there for hours.
The latest hostilities represent a serious setback in the effort to return refugees to Bosnia who were displaced during the 1992-95 war.
The NATO-led peace force evacuated aid workers and put more troops and helicopters on standby as a precaution against further rioting in the town.
In the night, international community officials succeeded in reaching an agreement between local Croats and Serbs.
The Croat side was represented by Slobodan Lang, senior advisor to Croatian President Franjo Tudjman.
"We have succeeded in stopping the particular problems, and we will help people to go to their homes or where they wish. Then there is the hard work to do, how to help people for that everybody is needed, any human being, everybody in the field whatever"
SUPER CAPTION: Slobodan Lang, Special Advisor to Croatian President Tudjman
The international delegation was led by Sir Martin Garrod, who said he was hopeful that a security agreement would be forthcoming.
"Today does have potentially very serious implications for the whole return program. And this must not be allowed to set the process back. It is crucially important that the process for return goes ahead. Not only for Croats, Bosnians and Serbs right throughout the whole of Bosnia Herzegovina. So we must not let a really serious day like this set the process back"
SUPER CAPTION: Sir Martin Garrod, International Community Official
Drvar was almost 100 percent Serb before the war but was taken over by Croat forces in 1995.
It now houses some eight-thousand Croats driven from homes elsewhere in Bosnia by the Serbs.
Croat refugees in Drvar and local hardline leaders have been trying to prevent the Serbs' return, staging incidents and burning houses.