ASSOCIATED PRESS WRITER

MARK PORUBCANSKY

SARAJEVO, Bosnia-Herzegovina (AP)—Bosnian Croats gave in Monday to U.N. demands and promised to allow aid this week to reach tens of thousands of Muslims trapped in Mostar, as heavy fighting reportedly raged in the city.

Bosnian Croat spokesman Veso Vegar, speaking from Mostar, told The Associated Press that a U.N. convoy would be allowed into the city’s eastern enclave on Wednesday.

Ron Redmond, a U.N. spokesman in Geneva, said there were 11 trucks ‘‘sitting across the border from Mostar, ready to go in at a moment’s notice.’‘

U.N. envoy Thorvald Stoltenberg in New York late Monday confirmed the Croats had given a go-ahead to deliver the aid.

The Belgrade-based Tanjug news agency, meanwhile, cited reports by Serb commanders on hills around Mostar as saying there was heavy fighting between Muslims and Croats in the city and many buildings were on fire.

About 55,000 Muslims have been under siege in eastern Mostar for weeks. Several thousand more Muslims live on the west bank of Mostar, controlled entirely by Croats until the Muslims established a bridgehead there last month.

U.N. peacekeepers who reached the Muslim area Saturday said residents were on the verge of starvation and hospital conditions were desperate.

Some operations were being performed without anesthesia, more than two-thirds of the residents were displaced, and 60 percent of the buildings were uninhabitable, they said.

Lyndall Sachs, spokeswoman for the U.N. High Commissioner for Refugees, told reporters the United Nations would split the contents of a 130-ton aid shipment between Mostar’s Croats and Muslims if allowed into the Muslim sector.

Croats and Muslims each made up some 42 percent of Mostar’s pre-war population of 130,000, and lived in peace. They united earlier this year to oppose Bosnian Serbs, but their alliance disintegrated a few months ago as plans for an ethnic division of Bosnia emerged.

Bosnia’s Croats want Mostar to be the capital of a Croat-dominated republic. Fighting between the city’s Muslim and Croat communities broke out in May.

Despite a Bosnian cease-fire signed Aug. 11 and last week’s peace talks in Geneva, sporadic fighting was reported across Bosnia on Monday. Along with the reported Mostar fighting:

_ Tanjug reported fierce fighting between Bosnian Croats and Muslims in disputed areas of central Bosnia. It said four Bosnian Croat soldiers and three civilians were killed. Croatian television reported heavy fighting between Croats and Muslims around Zepce, about 40 miles north of Sarajevo.

_ There were reports of Muslim-Serb clashes, especially in eastern Bosnia. Tanjug said Serbs were firing back on Muslim attackers ‘‘with full force.’‘ It said two Serb fighters had been killed. Bosnian radio reported Serb attacks on Brcko in the northeast, and on the town of Bradacac and the Gorazde region in the east.

The reports could not be confirmed.

In Sarajevo, the United Nations sent peacekeepers on Monday to press the Serbs to withdraw about 120 soldiers they have kept stationed a Mount Igman, which overlooks Sarajevo, despite a promise two weeks ago to pull back.

No information was available on the talks.

Bosnian President Alija Izetbegovic, a Muslim, has threatened to boycott the Geneva talks unless the Serbs withdraw.

In a potentially greater threat to the now-recessed Geneva talks, Izetbegovic has predicted that a special assembly would reject the latest peace plan to divide Bosnia. No date for the Bosnian assembly’s meeting has been announced, but sources speaking anonymously said it would likely be held Friday.

Under the plan supported by Serbs and Croats, Serbs would get about 52 percent of Bosnia, Muslims 31 percent and Croats 17 percent under a weak central government.

Muslims, who now control only about 10 percent of Bosnia, want at least 40 percent and demand that Serbs aren’t given land where they forcibly expelled Muslims.

Just hours after returning from Geneva Sunday, Izetbegovic called the plan unacceptable and indicated his beleaguered government would aim for a better deal. But he acknowledged the area accorded the Muslims was the most developed part of Bosnia.