Attacks From Croatia Threaten Truce, Bosnia Chief Says : Balkans: U.N. sees no violation because Serbs from neighboring state are not a party to accord.

Serbs from neighboring Croatia attacked Bosnian government troops Sunday, and the Bosnian president warned that a day-old truce would collapse unless the assaults stop.

The United Nations said the clashes were not violations of the truce, signed only by the Muslim-led government and Bosnian Serbs. But government leaders warned that the attacks by allies of the Bosnian Serbs could lead to wider fighting.

“If those attacks don’t stop, I am responsibly stating that there will be no cease-fire and that our army will respond on other fronts,” President Alija Izetbegovic told state radio.

The Croatian Serbs, who are not bound by the cease-fire brokered by former President Jimmy Carter, were attacking near Velika Kladusa, in the Bihac area in northwest Bosnia, U.N. officials reported. They were joined by Bosnian Muslim rebels who have been fighting the government for more than a year.

In another threat to peace efforts, Serbs in western Bosnia-Herzegovina declared a general mobilization “because of danger of Croatian aggression,” the Bosnian Serb news reports said.

Croatian army soldiers have joined Bosnian Croats fighting Bosnian Serbs in west-central Bosnia. The Croats and the Bosnian Croatians--allies of the Muslim-led Bosnian government--are not part of the cease-fire, either.

Most of Bosnia, however, was calm Christmas, a day after the cease-fire began, U.N. officials reported.

Spokesman Alexander Ivanko said there were 73 violations by the government army and 13 by the Serbs, but all were assessed as “celebration firing” because of the holiday season.

The first phase of the cease-fire lasts until Saturday and is meant to give time to work out a four-month truce.

Izetbegovic said the second phase couldn’t begin until peace came to Bihac.

“We are warning that if there’s no cease-fire, there will be no negotiations on the cessation of hostilities,” he said.

Negotiations for a lasting peace were already considered difficult because of disagreements over a multinational peace plan that the Serbs have repeatedly rejected.

The Bosnian government has insisted the Serbs accept the peace plan before negotiations begin on a lasting peace. The Serbs want to start negotiating without accepting the international proposal.