Philippine officials revealed on Thursday that their military forces had suffered a heavy setback in their fight against Islamist militants in Marawi City after a plane missed its bombing target and killed at least 10 government troops.

Defense Secretary Delfin Lorenzana told a news conference: "It's sad, but sometimes that happens. Sometimes in the fog of war, maybe the coordination was not properly done, so we hit our own people."

Read more: Amid Islamist takeover, death toll soars in besieged Philippine city

Seven more troops were also wounded in Wednesday's botched airstrike, although no civilians were reportedly hurt.

The military had been fighting the pro-"Islamic State” Maute group using a combination of ground troops and airstrikes from helicopters as it tried to flush militants out of buildings and drive them from the city. But for the first time on Wednesday, SF-260 close air support planes were deployed as well. 

"The first plane dropped the ordnance accurately, but the second one missed and hit our troops," Lorenzana said. "We are still investigating if there was a miscommunication, whether there was an error on the ground or in the air on the part of the pilot."

Following the incident, the Philippine military has deployed more ground troops and armored vehicles, indicating it could pull back on airstrikes. Lorenzana said he would leave that decision to the ground commanders, but added that he was confident the estimated 50 to 100 Maute fighters still holed up in the city "cannot hold that long."

Scores killed, tens of thousands displaced in Marawi City

Fighting in Marawi City broke out on May 23 after hundreds of Islamist militants seized buildings, stole weapons and released prisoners to join their fight in the city.

Read more: Seven terror organizations making headlines

Philippine President Rodrigo Duterte answered by declaring martial law in the region and launching a major offensive on the city, saying he was concerned that the southern Mindanao area could become a hotbed for Islamist extremism.

Around 120 rebel fighters have been killed in battles over the last nine days. Lorenzana also revealed on Thursday that officials had counted eight foreign nationals among the dead fighters, including people from Malaysia, Indonesia, Saudi Arabia, Chechnya and Yemen.

Wednesday's botched airstrike took the number of security forces killed to around 35.

Philippine officials claim that militants have killed 19 civilians in the crossfire, while insisting the military has not mistakenly killed any civilians. Roughly 100,000 people have fled the fighting.

dm/msh (AP, Reuters, dpa)