TIKRIT, Iraq At least 20 Sunni tribal fighters were killed in an air strike south of Mosul early on Wednesday when they were mistaken for Islamic State militants, Iraqi police said.
Whether the aircraft that carried out the attack belonged to the Iraqi air force or the U.S.-led coalition could not be determined.
A coalition official, Canadian Brigadier General D.J. Anderson, said in a news briefing on Wednesday that coalition planes conducted air strikes just after midnight on Wednesday on forces firing on Iraqi security forces near the town of Kharaib Jabr, south of Mosul.
"We are aware of the alleged reports that coalition forces mistakenly fired on Sunni tribal fighters," Anderson said. "We are looking into this to determine the facts that surround the case."
Both coalition and Iraqi forces are investigating the incident, Anderson said.
Local police and a tribal leader said the attack occurred around 1 a.m. (2200 GMT Tuesday) near Qayyara.
Qayyara is located 60 km (about 40 miles) south of Mosul, Islamic State's stronghold in northern Iraq.
Iraqi forces dislodged the militants from the town in August with support from the coalition, which plans to use a nearby airfield as hub to support the offensive on Mosul that could start this month, according to local commanders.
(Reporting by Ghazwan Hassan and Ahmed Rasheed; Additional reporting by Yeganeh Torbati in Washington; Writing by Maher Chmaytelli; Editing by Larry King and James Dalgleish)