An air strike has killed 19 pro-government tribal Sunni fighters near the town of Mosul, which is held by the Islamic State group, an Iraq tribal leader said.
Sheikh Nazhan al-Lihaibi said the air strike took place following hours of clashes between his troops and IS militants in the Haj Ali area to the east of the town of Qayara.
Mr al-Lihaibi said five more fighters were wounded.
The US-led coalition said it had carried out strikes in the area at the request of Iraqi security forces, adding that it had destroyed a building and killed eight enemy fighters.
"We are aware of the reports that Sunni tribal fighters were in the building that was struck and we are taking those reports seriously," a spokesman for the US-led coalition said.
He said the coalition and Iraqi security forces were carrying out a joint investigation into the incident.
Mr al-Lihaibi said his fighters had repelled an attack by IS late on Wednesday, and another two of his fighters had been killed in the clashes.
With aerial support from the US-led coalition, Iraqi government forces and paramilitary troops retook the town of Qayara in August.
The town, about 45 miles south of Mosul, is key for the long-awaited military operation to dislodge IS militants from Mosul.
Mosul, Iraq's second-largest city, is located about 225 miles north-west of Baghdad.
While the Syrian city of Raqqa is considered the caliphate's de facto capital, Mosul is the largest city under its control.
The Iraqi government is now gearing up for a major offensive to retake Mosul from IS. It pledged to recapture the city this year.