A U.S. bomb has gone astray in an attack in southern Afghanistan, and reports from the region say there are scores of civilian casualties, perhaps as many as 300.

Details of the incident remain scanty and confused. Pentagon sources say the errant bomb was dropped by a U.S. B-52 bomber during an attack on a cave complex north of the city of Kandahar that was suspected of being used by al-Qaida or Taleban fighters.

But other U.S. officials say the bomb went astray after an air reconnaissance patrol came under anti-aircraft fire. According to this version, the patrol called for combat air support, which unleashed an attack that included bombs against the anti-aircraft site. One of those bombs missed its target.

In either case, defense officials say they are aware of reports that the errant bomb caused civilian casualties, and they say an investigation is under way. But U.S. officials are not confirming local news reports that the bomb struck a wedding party where some of the participants may have been firing guns into the air in celebration.

One report by the Afghan Islamic Press puts the number of dead at 100 and the overall casualty toll, including wounded, at over 300.

The same report says U.S. forces were operating in the area, apparently in a continuing hunt for fugitive Taleban leader Mullah Mohamed Omar. The apparent accidental bombing is one of a series of combat mistakes reported since U.S. and coalition forces began anti-terrorist operations in Afghanistan in the wake of last year's attacks on the Pentagon and the World Trade Center.

In April, a U.S. aircraft mistakenly dropped a bomb on Canadian forces near Kandahar, killing four soldiers and injuring eight.