The U.N. commander in Bosnia warned Wednesday that NATO warplanes could be called in if government and Bosnian Serb forces don't stop trading artillery fire around Sarajevo.
In a letter to the rival military chiefs, Lt. Gen. Sir Michael Rose accused both armies of "serious breaches" of a heavy weapons exclusion zone 12.5 miles around the capital.And he warned of possible airstrikes if violations persist.
NATO imposed the exclusion zone in February. Although there have been violations, U.N. commanders have been reluctant to call in air power.
NATO jets did destroy an aging anti-tank weapon as a warning on Friday after Serb soldiers seized several heavy weapons from a U.N. collection site. The weapons were then returned.
Wednesday was the first time the United Nations issued such a direct warning to Muslim-led government forces, who have been defending Sarajevo against a Serb siege.
Airstrikes did not appear imminent. Rose's message seemed mainly a reminder that the exclusion zone applies to both sides.
An artillery duel north of Sarajevo prompted Rose's warning.
Peacekeepers say government troops have been firing into the zone from the north, while Bosnian Serbs have been firing north from inside the zone toward the government-held town of Visoko and other targets along a broad, fiercely contested front line.
Maj. Rob Annink, a peacekeeper spokesman, said NATO air strikes would be considered if the two sides continued to violate the no-weapons zone and rejected a proposal to deploy peacekeepers between the warring troops.
"We are worried," Annink said. "We want this to end."
Fighting north of Sarajevo, including sustained government offensives, made a mockery of a cease-fire agreement signed June 8, and extended for another month July 8.
The accord was not renewed this month. Yasushi Akashi, the top U.N. official in former Yugoslavia, expressed regret Wednesday that observance of the truce by both sides "has been far from satisfactory."
Annink reported intense shelling in areas along the broad front west and north of Sarajevo, including 400 rounds exchanged Tuesday around the town of Dastanko, 20 miles north of the capital.
Major troop movements were reported overnight, and a tank of unknown origin was spotted in the exclusion zone, Annink said.