MELBOURNE (Reuters) - An Australian air strike on Iraq in 2017 “may have” killed up to 18 civilians, the Australian government confirmed late on Thursday, following a year-long investigation.

Australia is part of the U.S.-led coalition fighting against Islamic State in Iraq and Syria.

Two Australian Super Hornets dropped bombs on a building and courtyard after Iraqi security forces had called for help to strike a neighborhood in west Mosul where Islamic State fighters had set up positions, the Defence Department said.

There was no specific intelligence suggesting civilians were at the targeted sites, but the Defence Department said “it was impossible to be sure under the urgent circumstances facing the Iraqi forces at the time,” adding that the Australian jet fighters hit their intended targets.

The Australian Defence Force was alerted by the U.S.-led coalition last January to claims on a website that tracks civilian deaths in war, Airwars, that there were civilians in a nearby building. Following an investigation completed in December, the Australian Defence Force concluded the claims were “credible.”

“Ultimately we have determined that it is possible civilians were unintentionally killed by the Coalition during these strikes,” Air Marshal Mel Hupfeld said in a statement. “Any loss of civilian life is highly regrettable and we treat all allegations seriously,” he said.

The coalition estimated that between six and 18 civilians may have been killed.

The coalition conducted 32,397 strikes in Iraq and Syria between August 2014 and the end of 2018, and estimates that at least 1,190 civilians were killed “unintentionally” in that period, the joint force said in a statement on Thursday.

Australia ended its strike aircraft operations in Iraq and Syria in January.