Manila, June 1 (IANS): Eleven Philippine soldiers were killed and seven others injured in a "friendly fire" incident in the city of Marawi, defence officials said on Thursday.

Brigadier General Restituto Padilla told the media here that the soldiers were killed and wounded in airstrikes aimed at Islamist militants on Wednesday, Xinhua news agency reported.

"One of our SF-260 aircraft was conducting an airstrike (when) the last ordnance round it (fired) went wayward for an unknown reason and accidentally hit our ground forces," Padilla said.

"This is a case of friendly fire. It was an accident." 

"Maybe the coordination was not properly done so we hit our own people. We don't know yet what exactly happened," he added.

Defence Secretary Delfin Lorenzana said the military is sending more troops to Marawi to fight the remaining 50 to 100 extremists still holed up in the embattled city.

The ongoing clashes have so far killed over 90 militants, including at least eight foreign fighters, 19 civilians and 36 security personnel.

On May 23, heavily-armed militants attacked Marawi -- which has a population of about 200,000 people -- when the military was searching for an Abu Sayyaf leader hidden in the city.