NAPLES, Italy -- NATO fighters shot down four Serb warplanes that had conducted a bombing raid over Bosnia on Monday in the first Western military intervention in the republic's conflict.


U.S. Admiral Mike Boorda, NATO commander in southern Europe, said the Yugoslav-built G-4 Galeb light attack planes twice ignored warnings to leave the UN's no-fly zone over Bosnia before U.S. F-16 fighters opened up with AIM heat-seeking missiles.


The action, shortly before 7 A.M. (9 A.M. Moscow time), marked the West's first military intervention in Bosnia's 22-month-old conflict and NATO's first combat action since it was founded in 1949.


In its first response to the incident, Russia, the main supporter of the Serbs, backed the alliance's downing of the planes but it said their identity was still uncertain.


A Foreign Ministry statement reported by Itar-Tass said, "Whatever side carried out the military sortie over Bosnia in violation of the corresponding UN Security Council resolutions on a no-fly zone, has to bear full responsibility for what has happened."


In recent weeks, the Russian government has sharply criticized a NATO threat to bomb Serbian artillery emplacements around Sarajevo, an issue that opened a rift between Moscow and the West.


Boorda told a news conference at his headquarters in Naples: "We reacted exactly as we told them we would. If it was a test, I think we passed the quiz."


NATO sources in Brussels said earlier the downed planes were operated by the Bosnian Serbs. "They were Serb planes and we think they took off from a base in Bosnia," said one source, who asked not to be identified.


A Bosnian Serb military spokesman in Belgrade denied that the planes were operated by Bosnian Serbs, saying no Galebs had flown from the Banja Luka base on Monday, but a Serbian military source in Pale, Bosnia, confirmed four Serb aircraft were shot down.


The United Nations canceled relief flights into Sarajevo and most land convoys in Bosnia had been canceled, apparently for fear of attack.


UN officials also said Serbs opened fire on the northern town of Tuzla several hours later. That could be in retaliation for the NATO action, or designed to prevent NATO and the UN from further pressing the Serbs by issuing an ultimatum to force open Tuzla airport.


"Just prior to the engagement the flight leader of the NATO fighters saw the Galebs make a bombing maneuver and saw explosions on the ground," Boorda said.


He said unconfirmed reports from UN forces in former Yugoslavia said "as many as eight bombs, perhaps more" hit targets which included a hospital and a storage facility.


In Zagreb, UN sources said the planes had apparently attacked a Moslem-controlled arms factory in central Bosnia, on the outskirts of Novi Travnik.


NATO agreed last April to enforce the UN-sanctioned no-fly zone to keep the skies over Bosnia-Herzegovina clear of all non-authorized flights to prevent the possibility of escalating the 2-year-old civil war.


Bosnian Serb leader Radovan Karadjic arrived in Moscow late Monday for talks with Russian officials on the Bosnian crisis. He declined to talk to reporters on arrival.


Meanwhile, Russia's extreme nationalist leader, Vladimir Zhirinovsky, denounced the NATO attack as a "provocation" and said the alliance should quit Bosnia.


Boorda said in Naples that Monday's incident was the first confirmed violation of the zone by fixed-wing aircraft since NATO began its Operation Deny Flight in April 1993.


He said the U.S. aircraft carrier Saratoga had cut short a call in the port of Trieste, northeast Italy, by 24 hours and was returning to duty in the Adriatic to enhance NATO's capability.


In Washington, President Bill Clinton said every attempt had been made to avoid the encounter. The United States was briefing "everyone involved in this effort to bring peace to Bosnia" on the situation, he told reporters.


(Reuters, AP)If it was a test, I think we passed the quiz."


NATO sources in Brussels said earlier the downed planes were operated by the Bosnian Serbs. "They were Serb planes and we think they took off from a base in Bosnia," said one source, who asked not to be identified.


A Bosnian Serb military spokesman in Belgrade denied that the planes were operated by Bosnian Serbs, saying no Galebs had flown from the Banja Luka base on Monday, but a Serbian military source in Pale, Bosnia, confirmed four Serb aircraft were shot down.


The United Nations canceled relief flights into Sarajevo and most land convoys in Bosnia had been canceled, apparently for fear of attack.


UN officials also said Serbs opened fire on the northern town of Tuzla several hours later. That could be in retaliation for the NATO action, or designed to prevent NATO and the UN from further pressing the Serbs by issuing an ultimatum to force open Tuzla airport.


"Just prior to the engagement the flight leader of the NATO fighters saw the Galebs make a bombing maneuver and saw explosions on the ground," Boorda said.


He said unconfirmed reports from UN forces in former Yugoslavia said "as many as eight bombs, perhaps more" hit targets which included a hospital and a storage facility.


In Zagreb, UN sources said the planes had apparently attacked a Moslem-controlled arms factory in central Bosnia, on the outskirts of Novi Travnik.


NATO agreed last April to enforce the UN-sanctioned no-fly zone to keep the skies over Bosnia-Herzegovina clear of all non-authorized flights to prevent the possibility of escalating the 2-year-old civil war.


Bosnian Serb leader Radovan Karadjic arrived in Moscow late Monday for talks with Russian officials on the Bosnian crisis. He declined to talk to reporters on arrival.


Meanwhile, Russia's extreme nationalist leader, Vladimir Zhirinovsky, denounced the NATO attack as a "provocation" and said the alliance should quit Bosnia.


Boorda said in Naples that Monday's incident was the first confirmed violation of the zone by fixed-wing aircraft since NATO began its Operation Deny Flight in April 1993.


He said the U.S. aircraft carrier Saratoga had cut short a call in the port of Trieste, northeast Italy, by 24 hours and was returning to duty in the Adriatic to enhance NATO's capability.


In Washington, President Bill Clinton said every attempt had been made to avoid the encounter. The United States was briefing "everyone involved in this effort to bring peace to Bosnia" on the situation, he told reporters.


(Reuters, AP)