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An explosion has been reported near the gate of the Philippine army's 104th Brigade headquarters, inside a karaoke bar on southern Jolo Island. At least 20 people are reported to have been injured. 

According to witnesses, most of the wounded were female entertainers, and men who were drinking at the bar.

U.S troops are encamped on the grounds for joint military exercises.

Security is a major concern for these exercises, mainly due to the presence of the Abu Sayyaf guerilla group, which is related to Al-Qaeda, and is stationed about 580 miles south of Manila.

Lt. Col. Mark Zimmer, a military spokesman said that no American deaths have been reported.