Smoke billows after a reported airstrike by the U.S.-led military coalition on Feb. 3 in the area of east Ramadi, Iraq. (Ahmad Al-Rubaye/AFP/Getty Images)

The U.S. military on Friday acknowledged killing 20 civilians and wounding 11 more in recent airstrikes in Iraq and Syria, more than doubling the number of civilian fatalities it has admitted causing in the military campaign against the Islamic State.

The nine errant airstrikes occurred between Sept. 10 and Feb. 2, U.S. Central Command said in a statement. Six of the strikes occurred in Iraq, and three occurred in Syria, U.S. military officials said.

“We deeply regret the unintentional loss of life and injuries resulting from those strikes and express our deepest sympathies to the victims’ families and those affected,” the military’s statement said.

The Pentagon had previously acknowledged killing an additional 15 civilians and wounding 15 in earlier airstrikes.

The latest disclosure came after Defense Secretary Ashton B. Carter announced this week that he would authorize sending an additional 200 military advisers to work with Iraqi military and deploy both Apache gunship helicopters and rocket artillery strikes in a planned offensive to reclaim the northern Iraqi city of Mosul from the Islamic State.

The casualties also were announced after Col. Steve Warren, a military spokesman in Baghdad, said Wednesday that the authority to launch airstrikes that could cause civilian casualties has been delegated to lower levels than when the military campaign began. Initially, those strikes had to be approved by the top commander for Central Command, but authority has since been given to Army Lt. Gen. Sean MacFarland, the top U.S. commander in Baghdad, or one of his deputy commanders, Warren said.

The most significant strike involving civilian fatalities acknowledged Friday occurred Oct. 5 in Atshanah, Iraq, near the city of Al Huwayjah, U.S. military officials said. Eight civilians were killed in a strike the U.S. military characterized as targeting a known position used by Islamic State fighters to launch mortars.

Five more civilians were killed Dec. 12 in the Iraqi city of Ramadi during an airstrike on what U.S. military officials described as a known Islamic State checkpoint after the civilians “unexpectedly moved into the target location after weapons already were in flight.” Another civilian in Ramadi died Nov. 12 during an airstrike targeting Islamic state fighters, U.S. officials said.

The other strikes that resulted in fatalities occurred in Kubaysah, Iraq, Sept. 10; near Raqqa, Syria, Dec. 10; in Tishreen, Syria, Dec. 24; in Mosul, Iraq, Jan. 11; and in Al Ghazili, Syria, Feb. 2. Two civilians died in the Kubaysah strike, and one each was killed in the other locations, U.S. military officials said.