The U.S.-led coalition that is launching airstrikes against the Islamic State in Iraq and Syria faces allegations that civilians have been killed in 71 separate strikes, according to Thursday reports.

A spokesman for U.S. Central Command (Centcom) said that allegations of civilian deaths have been made in 71 separate airstrikes since the campaign began last August, according to the Guardian. Many of the claims had been dismissed, but 10 reports had prompted formal investigations into the matter.

So far, the U.S. only acknowledges the deaths of civilians in one raid, when a Centcom investigation published in May found that a U.S. strike in Syria killed two children. Centcom only publishes investigations where a “preponderance of evidence” suggests the deaths of civilians.

In June, a report from the Syrian Observatory for Human Rights found that at least 162 civilians were among the 3,000 people killed during the aerial bombing campaign up to that month, including 51 children.

Another report from independent watchdog Airwars found last month that at least 459 civilians had likely died in the campaign. “Despite claims by the US-led Coalition that its airstrikes in Iraq and Syria are ‘the most precise and disciplined in the history of aerial warfare’, there are clear indications from the field that many hundreds of non-combatants have been killed by the 12 international allies in the first year of their air war against Islamic State,” the U.S.-based group said in August.

One of the worst alleged incidents took place in Iraq in June, when coalition aircraft bombed an ISIS explosives factory in the northern Kirkuk province, resulting in the deaths of 70 civilians, including 26 children.

Lt Gen John Hesterman, the U.S. commander in charge of the air campaign, said in June that the campaign was “the most precise and disciplined in the history of aerial warfare.”

Centcom divulged details of the investigation in response to questions about an internal document about fatality investigations obtained by conflict reporting website War is Boring, which gives details of alleged fatalities in 45 airstrikes.

A Centcom spokesman told the Guardian that investigating such allegations, especially within territory controlled by ISIS, is “extremely challenging.”

“Traditional investigation methods, such as interviewing witnesses and examining the site, are not typically available,” Cmdr Kyle Raines said. “We seek to investigate as thoroughly as possible given the limitations.”