MOSTAR, Bosnia-Herzegovina (AP) _ They should have been mingling freely in the town they once shared. But on the day the barriers were to come down, Muslims and Croats clung tenaciously to opposite sides of the Neretva River.

Serbs, Muslims and Croats once mixed with ease in Mostar. Then the war came, and though the guns are mostly quiet, the divisions linger.

Muslims and Croats are to share rule in the southern city of Mostar, according to the Bosnian peace accord, but the idea does not appear to be taking root: While Muslims want a unified city, Croats prefer to keep their links with Croatia proper, flaunting its flags, currency and symbols.

On Wednesday, tensions bubbled over.

Reacting to a proposal to establish a joint district in addition to three Muslim and three Croat areas, Croats attacked European Union administrator Hans Koschnick. They converged on his headquarters, surrounding his car and blocking his passage before NATO troops arrived. At least 10 bullets were fired into his armored car.

Later in the day, the mayor of the Croat side, Mijo Brajkovic, called the proposal a ``scam'' and announced on the radio that all ties with the EU mission had ended.

The usually optimistic Koschnick has threatened to resign and warned that the EU mission in Mostar could fail.

``Leading people of a nation may do one thing, and their people may do other things,'' he said.

The peace agreement puts 51 percent of Bosnia under Muslim-Croat control and 49 percent under Serb rule. But if Croats and Muslims cannot work with one another in places like Mostar, some wonder whether either side will be able to deal effectively with the Serbs.

Thursday was a critical day: Freedom of movement _ a key to Mostar's reunification _ was to have been restored. But amid the city's biggest snowfall in 15 years, not everybody was free to roam.

``Men of military age cannot get through,'' said Croat policeman Slavko Juric, who was manning a checkpoint. ``After yesterday's events ... things are a bit tense.''

Others, however, crossed the divide freely and fearlessly.

Sadeta Temim, a 55-year-old lawyer on the Muslim side who recalls the halcyon days before the war, crossed to the Croat side to visit friends.

``Of course I still have friends there,'' she said. ``What do you think? We go a long way back, longer than these people,'' Temim said, referring to the ruling hard-liners on the Croat side.

Like others her age, 15-year-old Jasmina Behran's most vivid memories are not of peace but of war. She describes the regular shelling in 1993 that sent her, her parents, and her little brother to a shelter.

``Sure, I go (to the Croat side) once in a while, to drink a juice, or see the shops,'' said the almond-eyed, slight teenager. ``But I really have no business there.''