SARAJEVO -- United Nations officials said Tuesday they were making progress in talks on a comprehensive cease-fire for Bosnia but the Moslem-led government insisted Serb operations in the Bihac enclave were jeopardizing the talks.


Bosnian vice president Ejup Ganic said his government would not discuss details of a proposed four-month cessation of hostilities until Serb forces from Croatia and Bosnia halted military activities in the northwest enclave of Bihac.


Ganic, who met Bosnia's UN commander Lieutenant General Sir Michael Rose, said his government was demanding the withdrawal of Croatian Serb forces from the enclave and an end to alleged Bosnian Serb attacks as "the condition for further negotiations."


But UN spokesman Alexander Ivanko told reporters negotiations were continuing on pace on an extensive four-month cessation of hostilities, despite public statements from the Bosnian government.


"We consider that discussions (with the government) are ongoing although at an informal level currently," Ivanko said. "We still hope that the position of the Bosnian government will not derail the peace process."


Ivanko said talks held Monday with both sides had proved "positive and useful" and that the UN was preparing a fresh draft of a proposed cessation of hostilities accord.


A seven-day cease-fire brokered by former U.S. president Jimmy Carter has slowed fighting significantly across Bosnia since it began Saturday.


UN officials want to take advantage of the truce to negotiate an accord for a four-month cessation of hostilities and a resumption of peace talks aimed at ending the 33-month-old war in the former Yugoslav republic.


But the latest cease-fire pact was not signed by Croatian Serb and rebel Moslem forces attacking government troops in the Bihac enclave. The United Nations Protection Force reported mostly sporadic firing in Bosnia while the Bihac enclave remained tense.


Nine detonations were reported east of Bihac town on Monday and a dozen shells or mortar bombs landed southwest of Velika Kladusa, in the north of the Bihac enclave, UNPROFOR said.


Ganic accused Serb forces of trying to tighten their hold on Kladusa, which fell into Serb and rebel Moslem hands earlier this month. "They are trying to enlarge their presence in Velika Kladusa and we are trying to stop them," said Ganic.


Bosnian government troops were badly mauled by an allied Bosnian and Croat Serb counter-offensive in November that enabled rebel Moslems to recapture Velika Kladusa.


The UN said aid convoys were allowed free movement generally through Bosnia but Croatian Serbs and rebel Moslems were still obstructing regular food deliveries to the Bihac enclave.


A UN food convoy reached the town of Cazin in the Bihac enclave Tuesday after Serb and rebel Moslem forces held up the convoy for five days, said Peter Kessler, a spokesman for the United Nations High Commissioner for Refugees. Shooting and shelling in and around Sarajevo has subsided since the Christmas eve truce went into effect.