A Philippine airstrike targeting Daesh-affiliated militants in the country's south has missed its target and mistakenly killed two soldiers, the army says.

Lieutenant Colonel Jo-Ar Herrera, a military spokesman, said in a statement on Wednesday that the soldiers were killed when a fighter jet pounding militant positions in the city of Marawi missed its target and bombed buildings.

Large debris from heavily reinforced buildings accidentally hit two of our personnel, Herrera said.

The air raid also left 11 other soldiers slightly wounded after being hit by shrapnel.

 We are saddened by this unfortunate incident, said the military spokesman.

The incident is the second of its kind in a fatal campaign to purge the city of the militants. On May 31, eleven government troops lost their lives in a similar raid.

On May 23, the Maute militant group, which was founded some five years ago and pledged alliance to the Takfiri Daesh terrorist group in April 2015, overran parts of Marawi City, the capital and largest city of the province of Lanao del Sur on the island of Mindanao in the southern Philippines, and since then, it has been at the forefront of a vicious battle with the government forces, deployed to eliminate the group's members in the city.

President Rodrigo Duterte said on Tuesday that his forces needed 15 more days to defeat the terrorists.

More than 500 people, including 389 militants, 90 soldiers and policemen, and 39 civilians, have been killed since the fighting broke out. About 260,000 residents have been forced to flee from the city.