U.N. Finds Bosnia Town Devastated : Siege: Fewer than 250 of Zepa’s 40,000 residents and refugees remain in Muslim enclave after fierce Serb artillery attack. Bosnian Croats, Muslims still battle in Mostar.

U.N. military observers entered the besieged Muslim enclave of Zepa in eastern Bosnia-Herzegovina on Monday to discover widespread destruction and fewer than 250 people left in a town of about 40,000 residents and refugees.

The reports relayed to U.N. peacekeeping headquarters in Zagreb, Croatia, were the first independent confirmation of claims by the Muslim-led Bosnian government in Sarajevo that Zepa was the target of a fierce Bosnian Serb artillery attack that began last week.

U.N. officials said 10 bodies were discovered in a mosque and that of the 250 living, 200 were wounded and had been left behind by the masses who fled the Serbian onslaught.

The U.N. observers in Zepa reported that most residents had fled the town and were living in huts, makeshift tents or in the open, the Associated Press said.

About 100 U.N. peacekeepers arrived later Monday and were expected to organize an airlift of the wounded today.

The troops were dispatched to demilitarize the town in accordance with a cease-fire agreed to by Bosnian Serb and government forces. But they found the town nearly deserted except for the wounded and a few dozen people too old to flee.

“They discovered that most of the buildings and houses were badly damaged by artillery fire and that most of the people had fled to the nearby forests,” Dalgeed Bagga, a spokesman for the U.N. mission in Zagreb, said of the military observers’ reports.

In the south of the war-torn former Yugoslav republic, Bosnian Croat and Bosnian government officials proclaimed a cease-fire in Mostar, scene of the latest flare-up of fighting between the former allies. But a U.N. source said there was no sign of a letup in shooting in the Croatian stronghold after the truce took effect at 6 p.m. local time.

More than 1,000 Muslim women and children were rounded up by Bosnian Croat troops Sunday and bused out of Mostar in what U.N. officials believe to have been an exercise in “ethnic cleansing,” the forcible displacement of civilians practiced by all parties in the conflict but most frequently by Bosnia’s rebel Serbs.

The commander of U.N. forces in the former Yugoslav federation, Gen. Lars-Eric Wahlgren, called for an investigation into the whereabouts of the Muslims, who made clear to Spanish U.N. peacekeepers in Mostar that they were being forcibly taken away.

“The safety of civilians--including refugees--caught up in this fighting must be guaranteed,” Wahlgren said. “It is a matter of utmost urgency to find out what has happened to these hundreds of people who have been taken from Mostar.”

U.N. officials have accused the Bosnian Croat military forces, known as the HVO, of instigating the latest fighting with a dawn attack Sunday on Muslim areas of the city. Mostar was predominantly Muslim before the war but surrounded by towns and villages peopled by ardently nationalist Croats.

Encouraged by the Bosnian Serbs’ success in creating ethnically pure territory in the republic’s east, Croatian hard-liners have lately sought to strengthen their hold on the southwestern region by expelling the remaining Muslims or terrorizing them until they flee.

At least 250 died in Croat-Muslim fighting last month that U.N. troops blamed largely on the HVO.

Artillery and small-arms fire was so intense in Mostar on Sunday that most of the Spanish troops deployed in the city retreated to the outskirts for their own protection. HVO forces have refused to let other U.N. troops enter.

In the case of Zepa, peacekeepers had been trying without success to enter the enclave since Sarajevo officials appealed for its protection when it came under heavy fire Thursday.

Zepa, Srebrenica and Gorazde are the last three Muslim areas of eastern Bosnia, which has otherwise been overrun by Serbian nationalists rebelling against the republic’s March, 1992, vote to secede from Serb-dominated Yugoslavia.

The Zepa attack began shortly after the Bosnian Serbs’ self-declared parliament rejected a Western-mediated peace plan, stepping up pressure for foreign military intervention to halt the violence that has left more than 150,000 killed or missing over the past year.

Mediators Cyrus R. Vance of the United Nations and Lord Owen of the European Community have proposed dividing Bosnia into 10 ethnic provinces as a means of curbing the bloodshed.

Bosnia’s Muslims and Croats have endorsed the Vance-Owen plan, but the Serbs have repeatedly refused because it would call an end to their campaign to create a Greater Serbia from the conquered areas of Bosnia and Croatia and from the rump Yugoslavia.

Even Serbian President Slobodan Milosevic, the main instigator of the Greater Serbia drive, has lately tried to distance himself from the intransigent Bosnian Serb leadership in an attempt to get severe U.N. sanctions lifted from his own country and to avoid becoming a target of threatened Western military intervention.

Milosevic announced after the latest Bosnian Serb vote against the peace plan last Thursday that his republic would cease all supplies to the rebels with the exception of food and medicine.

Reports from U.N. observers at the Yugoslav-Bosnian border suggest there has been a falloff of obvious support, and at least one key figure from the Bosnian Serb leadership was turned away from the border in an ostensible snub by Belgrade.

Biljana Plavsic, the hard-line nationalist vice president of the Bosnian Serbs’ self-proclaimed republic, told Belgrade Television late Sunday that she had been denied entrance at one Yugoslav border crossing but managed to get to the capital, Belgrade, by means she declined to detail.