A U.S. Army spokesperson said at least one Muslim man was killed and approximately 10 people were injured during the clash, which lasted most of the day. The spokesperson, Sgt. Maryanne Mirabella, said she could not confirm reports that Serb gunners fired mortars on a crowd of Muslims seeking to return to their village.
The fighting between the villages of Celic, in Muslim territory, and Koraj, occupied by the Serbs, underscored the fragility of the peace agreement reached at Dayton, Ohio, nearly a year ago. It erupted just as NATO leaders and Western powers are considering whether and how to extend NATO's mandate in Bosnia to keep a shaky peace.
NATO officers said the clash, on a road U.S. soldiers call Route Kansas on the rolling plains of northwestern Bosnia 60 miles northeast of Sarajevo, was a model for how the peace could unravel more than a year after guns fell silent in a cease-fire declared in October 1995.
Mexico City officials have been declaring a record number of smog-emergency days - four in row recently. Many here fear that the coming months - Mexico City's smog season - will rank among the city's worst ever.
And environmentalists are pointing to neighborhoods such as El Zacaton as a principal cause.
The cloud spread across the horizon, burning eyes and lungs even up in fast-growing El Zacaton - the Pasture, where construction workers, oblivious, continued carving the city deeper into one of its few remaining forests, illegally building makeshift homes to accommodate a population boom that brings 1,000 new residents to Mexico City each day.
Officially, city authorities say the pollution problem, though bad, is so far statistically no worse than in recent years. They blamed the weather for the recent string of smog emergencies - the most on consecutive days since an air-quality alert system was put in place six years ago.
Yet even during the last week of below-emergency readings of ozone - a chemical that protects humans from harmful ultraviolet light in the stratosphere but makes daily life miserable at ground level and may cause serious health problems - remained above accepted norms almost every day.
In more than a dozen interviews and thousands of pages of recent studies, Mexican and U.S. scientists agreed that the most direct causes of Mexico City's toxic cloud are as many and varied as the alphabet soup of chemicals swirling inside it. But they also agreed that efforts to contain it, especially amid the lasting impact of Mexico's economic crisis, are a case study in environmental frustration.
"So now there are fewer options for people to be responsible about fighting pollution," said Pedroza, the chief pollution monitor. "And every day, more people are coming to live in the city."
Urban planner Jorge Legorreta said that new arrivals from the impoverished countryside settle first in poor inner-city districts, where they rent bed space while working in menial jobs to save money. Later, many go to the city's outskirts to build a small home and settle.
El Zacaton, on the metropolitan area's extreme southern fringe, is a case in point. Ten years ago, shop owner Martinez recalled, the neighborhood had just eight houses. Today, there are hundreds - and hundreds more on the way - most of them encroaching on an officially sanctioned ecological reserve.
"Yeah, they've torn out the trees," said Martinez, who migrated here from the impoverished southern state of Oaxaca in 1978 and built his shop and home in El Zacaton three years ago.
El Zacaton's residents steal electricity through a spaghetti-like snarl of cables connected to a legal settlement across the road, and many have fraudulent deeds to "their" land.
Despite occasional bulldozing of the illegal new colonies by city officials, most spring up again within months. And the city's latest development plan appears to give up on the idea of urban containment. It envisions a "megalopolis" that extends more than 100 miles from Cuernavaca in the south to the state of Hidalgo in the north.
Yet even in the face of such mind-boggling growth, not all scientists are pessimistic. Much of that development is expected to take place beyond the mountain ranges that help contain the capital's smog, which would help diffuse the pollution sources.