Serbs Shell Croatian City, Threaten Capital in Dispute Over Bridge : Balkans: Ceremonial reopening of span is planned. U.N. sources warn of rekindling of deadly conflict.

Serbian militants in the occupied Krajina region Thursday launched their most punishing assault in Croatia since late 1991, blasting more than 70 shells into this front-line city and threatening to attack the nearby capital of Zagreb with Scud-type missiles.

U.N. sources warned that the attack, provoked by Croatian government plans to reopen a strategic bridge near the Adriatic Sea this weekend, could signal a full-scale rekindling of the Serb-Croat conflict that killed 10,000 people two years ago.

“As we have seen in this nasty little war in Krajina, neither side hesitates to target civilian centers,” said Cedric Thornberry, deputy chief of the U.N. Protection Force in the former Yugoslav federation.

The shelling of Karlovac was the most serious assault on a Croatian city since a U.N.-brokered cease-fire went into effect 18 months ago and reduced fighting to occasional skirmishes within the U.N.-patrolled Krajina sector.

Eight people were injured in the pre-dawn barrage, sending residents to their cellars for the first time in months until the artillery went quiet at the break of day.

The International Red Cross announced it was pulling out of Croatia temporarily because of the shelling at Karlovac, where it runs a transit center for refugees.

Serbian nationalist forces opposed to Croatian independence also shelled the Adriatic port of Zadar and several villages in the Dalmatian hinterland around the town of Maslenica.

The Croatian government has built a pontoon bridge at Maslenica to replace a vital link destroyed when the Serbian separatists overran the area two years ago.

Croatian government troops recaptured the territory surrounding the ruined bridge in a Jan. 22 offensive that violated the U.N. cease-fire and prompted a Security Council resolution ordering the Croats to pull back.

Instead, an 825-foot pontoon bridge has been laid to restore the key crossing that links the interior of Croatia with the ports and resorts on the Dalmatian coast.

Croatian President Franjo Tudjman plans a ceremonial reopening of the span Sunday, despite warnings from angry Serbian rebels that they will attack the new bridge. On Thursday, the U.N. Security Council urged Croatia to scrap the ceremony.

Tudjman refused an offered compromise that would have reopened the bridge under U.N. supervision and with the approval of both the Krajina rebels and Serbian President Slobodan Milosevic, in exchange for a token concession to the Serbs on an unrelated civilian matter, one U.N. source disclosed privately.

“The bridge could have been operating with the Serbs’ blessing. All Tudjman had to forgo was the ceremony,” said the official, adding that both sides seemed to have decided to risk another war.

Heavy buildup of troops and artillery has been reported throughout the Krajina region, which is under nominal U.N. supervision but effectively under Serbian rebel control.

Serbian authorities in the rebel stronghold of Knin, Krajina’s self-styled capital, have positioned Frog missiles--similar to the Scud--in range of Zagreb and have threatened to attack the capital if the bridge is unilaterally reopened, the official said.

Krajina Serbs have openly warned that they will consider restoration of the bridge a military provocation and have written to U.N. Secretary General Boutros Boutros-Ghali to ask that U.N. forces intercede.

“This is our last appeal to prevent the flames of war,” said the rebels’ letter, as reported by the Belgrade-based Tanjug news agency.

The bridge is crucial to the Croatian economy. The resort-rich southern Dalmatian coast is now accessible from the interior only by ferry via the desolate island of Pag, because the Serb forces hold one third of this republic and prevent passage through the vast region that extends nearly to the coast south of Zadar.

In addition to the impending bridge ceremony, Krajina Serbs likely have also been inflamed by a deadly act of sabotage against a passenger train.

Four people were killed and 27 were wounded Wednesday when the train passed over a small bridge west of the town of Glina, setting off an antitank mine planted under the span, said U.N. spokeswoman Shannon Boyd.

The United Nations has not determined which side targeted the train. But because it was a Serbian conveyance and the explosion occurred just inside the front line, it was widely believed to have been the work of Croats.