THE conflict in former Yugoslavia has threatened to escalate to new heights as military tensions have increased between the West and ethnic Serbs, this time in Croatia.
UN approval of NATO airstrikes on the Serb-controlled Krajina region of Croatia came Saturday after Croatia's Serbs attacked the Muslim-held town of Bihac in Bosnia-Herzegovina by air.
The town is a United Nations ``safe area,'' one of six Muslim-dominated enclaves in Bosnia designated by the UN to protect civilians from Bosnian Serb forces.
In the surrounding region, also known as Bihac, Muslim-led Bosnian troops are battling to repulse Bosnian Serb forces backed by Croatian Serbs.
Croatian Serbs vowed to respond with ``military means'' to NATO airstrikes and implied that they would attack both targets in Croatia and UN Protection Force (UNPROFOR) peacekeeping troops deployed on truce lines in the former Yugoslav republic.
Rebel Croatian Serb leader Milan Martic warned the UN that NATO attacks would constitute ``fresh Croatian aggression and UN siding with Croatia.''
The warning led some UN officials to believe that Mr. Martic and his Bosnian Serb allies had deliberately staged the air attacks on Bihac in order to reignite fighting in Croatia that was stilled by a shaky March 28 cease-fire.
Escalating the war, the officials say, would be the most effective way to kill the ``contact group's'' peace plan for Bosnia, which was rejected by the Bosnian Serbs.
The contact group consists of the US, Russia, Britain, France, and Germany.
Drawing Croatia back into battle would also halt international efforts to broker economic and political accords to restore Zagreb's control over the third of its territory the rebel Serbs captured and declared as their own independent state in 1991.
On Saturday, Croatian Serbs rejected an agreement on reopening utility and road links between their territories and the rest of Croatia. Zagreb had agreed to sign the accord.
Finally, an escalation in the war could force Serbia's President Slobodan Milosevic to reverse his backing of the international peace efforts and restore the military and political support he withdrew from his estranged Bosnian Serb proxies.
``Milosevic would be put in a very uncomfortable position,'' a UN official says.
Mr. Milosevic won an easing of UN sanctions last month by allegedly cutting off strategic supplies to the Bosnian Serbs. The contact group is now considering a plan under which it would further lift the sanctions if Milosevic recognizes the international borders of Bosnia and Croatia.
That would put an end to the goal of the Bosnian Serbs and their rebel Croatian kin of uniting their territories with Serbia and Montenegro in a ``Greater Serbia.''
The UN Security Council voted 15 to 0 in New York on Saturday to allow NATO airstrikes in Croatia's Serb-held Krajina region. The decision was later endorsed by the Brussels-based North Atlantic Council, the executive body of NATO.
Under the UN resolution, NATO jets can pursue into Croatian airspace - for a one-week period agreed to by Zagreb - planes that violate the UN-decreed ``no-fly'' zone over Bosnia or hit bases from which they take off.
US officials had pressed for a NATO strike on the former Yugoslav Army's airfield at Udbina, a mountain-ringed base near Krajina's border with the Bihac region, where the jets took off from Friday and Saturday to attack the Bihac enclave.
``Let us be clear. What we are witnessing is a pattern of activity from the Udbina airfield that places at risk the safe area of Bihac, civilians in the Bihac pocket, and UNPROFOR troops deployed there,'' United States Ambassador to the United Nations Madeleine Albright told the Security Council.
``My government believes that this pattern of military activity justifies a military response from NATO,'' said Mrs. Albright, the current council president.
The unified UN vote appeared to slightly heal a rift within the contact group that erupted when President Clinton earlier this month ended UN enforcement of the UN arms embargo on the Muslim-led Sarajevo government.
The move provoked Britain, France, and Russia to vote anew on Friday to withdraw their UN troops from Bosnia if the embargo is lifted.
UN officials said Saturday's air attack on the Bihac enclave appeared aimed at a munitions factory in the town of Cazin.
One plane, however, hit a chimney and plowed into an apartment building that housed refugees. It exploded, killing the pilot, setting the building aflame, and scattering undetonated bombs.
Reports put casualties at between nine and 15. The second plane immediately dropped its bombs, which exploded harmlessly near the building, and returned to Udbina, they said.
On Friday, two aircraft dropped napalm and cluster bombs close to the Bosnian Army Fifth Corps' headquarters in Bihac town. There were no casualties. The napalm bomb, the first used in the Yugoslav conflict, did not explode and was recovered by UN troops.
The Bihac pocket is located in Bosnia's northwestern corner, wedged between Bosnian Serb-held land and the Croatian Serb-controlled Krajina.
Almost a month ago, the Fifth Corps broke out of the pocket and captured 90 square miles of territory, most of which it has since lost to a Bosnian Serb counterattack. The enclave's fall would remove an obstacle to the unification of Bosnian Serb- and Croatian Serb-held lands.
Fighting has escalated in central and western Bosnia, where the Bosnian Army and its Bosnian Croat allies battle to expand recent territorial gains that have put the Bosnian Serbs on the defensive for the first time since the war erupted in March 1992.