WASHINGTON -- The U.S. military said Thursday it is investigating last weekend's raid by U.S. special operations forces in Yemen and that innocent civilians, including children, were apparently killed.

U.S. Central Command said civilians may have been hit by gunfire from aircraft called in to assist U.S. troops, who were engaged in a ferocious firefight with militants from al-Qaida in the Arabian Peninsula, the group's Yemen affiliate.

The military said the civilians may not have been visible to the U.S. forces because they were mixed in with combatants in the compound who were firing at U.S. troops "from all sides to include houses and other buildings."

The Pentagon disputed published reports that the operation was compromised and that U.S. troops lost the element of surprise in the assault on the compound.

"We have no information to suggest that this was compromised," said Navy Capt. Jeff Davis, a Pentagon spokesman, saying the accounts do not "match with reality."

He said the U.S. special operations forces conducted the raid to get valuable information and intelligence, including about potential operations by al-Qaida against the United States and the West.

The plan, he said, was to "go in, conduct a raid, grab things and go." When the firefight broke out, he said the team "needed to call in this support in order to ensure that they could get out and not lose their lives." Fighter aircraft and helicopters responded to provide cover from the air for the forces, which included a Navy SEAL team.

Nasser al-Awlaki told The Associated Press that among the children killed was his 8-year-old granddaughter Anwaar, an American citizen. Her father was Anwar al-Awlaki, a radical Yemeni-American cleric killed in a U.S. airstrike in Yemen in 2011.

The grandfather said Anwaar was visiting her mother when the raid took place, and was shot in the neck and bled to death. The Pentagon hasn't confirmed the young al-Awlaki was killed in Sunday's raid.

"Al-Qaida in the Arabian Peninsula has a horrifying history of hiding women and children within militant operating areas and terrorist camps, and continuously shows a callous disregard for innocent lives," said Col. John J. Thomas, U.S. Central Command spokesman.

Navy SEAL William "Ryan" Owens was killed in the assault, and three other U.S. service members were wounded. Another three U.S. forces were wounded in the "hard landing" of an MV-22 Osprey aircraft at a staging area for the mission.

According to Central Command, the firefight included small arms fire, hand grenades and close air support fire.

Davis said earlier this week that an unspecified number of women were part of the group of combatants battling the U.S. forces, and some were among the 14 killed in the firefight.

Planning for the clandestine counterterrorism raid began before President Barack Obama left office on Jan. 20, but President Donald Trump authorized the raid.

White House press secretary Sean Spicer said Thursday that Central Command submitted plans for the raid to the Defence Department on Nov. 7, and it was approved in an interagency deputies meeting on Jan. 6. At the time, the plan called for the raid to take place on a moonless night, Spicer said, which meant it couldn't happen until after Trump's inauguration.

He said Defence Secretary Jim Mattis supported the raid, and Trump approved it on Jan. 26.

The U.S. has been striking the militant group from the air for more than 15 years, mostly using drones. Sunday's surprise pre-dawn raid could signal a new escalation against extremist groups in the Arab world's poorest but strategically located country.

Associated Press writer Ken Thomas contributed to this report.