TWO US jets policing the UN-decreed ``no-fly'' zone over Bosnia-Herzegovina yesterday shot down four Bosnian Serb aircraft in the first foreign military intervention of the 23-month-old conflict, United Nations and NATO officials said yesterday.
It was the first action to enforce the 1 1/2-year-old UN resolution establishing the air exclusion zone, and also the first offensive action taken in NATO's 44-year history.
There was no immediate confirmation from the Bosnian Serbs, but John Zametica, spokesman for Bosnian Serb leader Radovan Karadzic said, ``This shows that NATO is oriented exclusively toward strikes on Serbian targets. It is well known that in the area of Travnik and Bugojno there are no Serb troops, but only Croats and Muslims.''
The incident threatened to darken the slim glimmer of hope for progress toward a settlement to the war that was generated by the new involvement of the United States and Russia as mediators between the warring factions.
Apparently mindful of possible new tensions with his Russian counterpart, Boris Yeltsin, President Clinton insisted to reporters in Washington that the US pilots made ``every attempt'' to avoid shooting at the Bosnian Serb jets.
There were concerns that the downings would provoke an escalation in fighting as Bosnian Serbs sought to exact vengeance. Those concerns were underscored by what UN officials called a retaliatory Bosnian Serb artillery attack launched against the airport in the besieged Muslim-led government stronghold of Tuzla.
No injuries were reported among UN troops deployed at the airport, which the Bosnian Serbs have refused to open to UN humanitarian relief flights.
Elsewhere, Bosnian Serb tanks moved in the Sarajevo area, defying a NATO threat to launch airstrikes against any heavy artillery found after Feb. 20 within 13 miles of the capital and not under UN control.
Bolstered by the NATO ultimatum and the deployment of UN peacekeeping troops on its front lines, the city has enjoyed a virtually incident-free cease-fire since Feb. 11.
The UN High Commissioner for Refugees cancelled aid flights into Sarajevo and land convoys that provide food and medicines for hundreds of thousands of people trapped by the conflict that has claimed an estimated 200,000 lives. Western officials warned the Bosnian Serbs against attacking troops of the UN Protection Force (UNPROFOR) in retaliation for the downing of their jets.
UN and NATO officials identified the Bosnian Serb jets as Yugoslav-made Super Galebs. They were shot down by two US F-16 ``Flying Falcons'' at 6:48 a.m. local time near Novi Travnik, about 40 miles northeast of Sarajevo, officials said. The four Super Galebs were among six Bosnian Serb jets that had just attacked the Bosnian government-controlled Bratstvo munitions plant in Novi Travnik, UN officials said.
A statement issued by NATO headquarters in Belgium said the US pilots twice informed the Bosnian Serb aircraft by radio that they were violating the ``no-fly'' zone and ordered them to land. ``The [US] pilots issued, in accordance with their rules of engagement, two `land or be engaged' orders to the aircraft, which ignored them,'' the statement said. ``The NATO Flying Falcons engaged the planes, shooting down four of them.''
Novi Travnik has been the scene of fighting for months between the Muslim-led Bosnian Army and Bosnian Croat forces, which are effectively surrounded in part of the town.
UN sources in Belgrade, speaking on condition of anonymity, said aircraft from Croatia's tiny airforce were also involved in attacking the munitions factory. There was no immediate confirmation of this, and Croatian officials denied involvement.
WHETHER Croatia was involved or not, the fact that Bosnian Serb aircraft were operating in the Novi Travnik area provides the strongest proof yet of military cooperation between the Bosnian Serbs and the Bosnian Croats.
Serbia and Croatia, which fund and arm the ethnic Serb and Croat forces in Bosnia respectively, have long been suspected of secretly agreeing to carve up the former Yugoslav republic at the expense of the Muslims, its largest community.
The new development held unknown consequences for peace talks between the Bosnian government and Bosnian Croats that Clinton officials began brokering in Washington last weekend.
Russia, traditionally linked to the Serbs through their common Slavic ethnic origins and Orthodox religion, expressed anger at being excluded from the talks. Moscow's entry as a major player in the Balkans embroglio was marked by its agreement to provide Russian troops to UNPROFOR units policing the Sarajevo cease-fire.
The deployment of Russian soldiers gave Bosnian Serb leader Radovan Karadzic the face-saving formula he needed to comply with the NATO ultimatum.
In Moscow, a Foreign Ministry official said that Mr. Karadzic would be visiting yesterday for talks with senior Rusian diplomats on the situation in Bosnia.
US, French, British, Turkish, and Dutch aircraft based in Aviano, Italy, are participating in NATO's ``Operation Deny Flight,'' which began in April 1993. President Clinton, however, said that Monday's incident involved the first ``fixed-wing violation. ``Those are much more serious because the capacity they have to engage in military conduct from the air ... the war could be carried into the air,'' he told reporters.