Report: Airstrikes in Iraq and Syria kill 459 civilians, 15,000 militants

US-led airstrikes targeting the Islamic State group in Iraq and Syria have likely killed at least 459 civilians and more than 15,000 militants in the past year, a report by an independent monitoring group said on Monday.

The report by Airwars, a project aimed at tracking the international airstrikes targeting the extremists, said it believed 57 specific strikes killed civilians and caused 48 suspected "friendly fire" deaths.

While Airwars noted the difficulty of verifying information in territory held by the IS group, which has kidnapped journalists and activists, other groups have reported similar casualties from the US-led airstrikes.

"Almost all claims of noncombatant deaths from alleged coalition strikes emerge within 24 hours with graphic images of reported victims often widely disseminated," the report said.

"In this context, the present coalition policy of downplaying or denying all claims of noncombatant fatalities makes little sense, and risks handing Islamic State and other forces a powerful propaganda tool."

The US launched airstrikes in Iraq on Aug 8 and in Syria on Sept 23 to target IS. A coalition of countries later joined to help allied ground forces combat the extremists. To date, the coalition has launched more than 5,800 airstrikes in both countries.

The US has only acknowledged killing two civilians in its strikes: two children during a US airstrike targeting al-Qaida-linked militants in Syria last year. That same strike also wounded two adults, according to an investigation released in May by the US military.

That strike is the subject of one of at least four ongoing US military investigations into allegations of civilian casualties resulting from the airstrikes. Another probe into an airstrike in Syria and two investigations into airstrikes in Iraq are still pending.

US Army Colonel Wayne Marotto, a spokesman for the coalition, did not address the report directly, but said, "There is no other military in the world that works as hard as we do to be precise."

"When an allegation of civilian casualties caused by Coalition forces is determined to be credible, we investigate it fully and strive to learn from it so as to avoid recurrence," he said.

Navy Captain Jeff Davis, a Pentagon spokesman, said the department has seen the news reports on the additional civilian casualties, but said the Pentagon will have nothing to say until the reports are reviewed.