ZAMBOANGA, Philippines, June 17: Unknown gunmen opened fire at US troops on Monday on an island stronghold of Muslim rebels in the southern Philippines, but no one was injured, Philippine military officials said.

It was the first known attack on the US forces which have been on Basilan island since February to train Filipino soldiers in fighting the Abu Sayyaf guerrilla group, linked by the United States to Osama bin Laden and his al Qaeda network.

The US troops, numbering about 1,000, include special forces as well as military engineers building roads and airstrips on Basilan, a jungle-clad island 900 km (560 miles) south of Manila.

“There was an ambush involving American troops... No one was injured in the shooting,” a senior Filipino military officer said by phone.

A US military spokesman confirmed there had been a shooting incident.

“All we have are reports that there was gunfire that occurred in the vicinity of one of our worksites. We are still investigating the report,” US Air Force Major Richard Sater told Reuters.

The incident came 11 days after US missionary Martin Burnham and a Filipina nurse, held hostage for more than a year by the Abu Sayyaf, were killed during a military rescue operation in the forests of Zamboanga del Norte, near Basilan. Burnham’s wife, Gracia, was wounded but rescued in the operation.

The military sources said Monday’s attack was launched just before 6 p.m. in the village of Kumalarang, where the Abu Sayyaf has strong popular support. The village lies on the outskirts of Basilan’s provincial capital of Isabela.

Shortly after the incident occurred, two US Army Chinook helicopters flew out of the Zamboanga air base towards Basilan on an unknown mission.—Reuters