U.S.-led air strikes targeting the Islamic State group in Iraq and Syria have likely killed at least 459 civilians over the past year, an independent monitoring group said August 3.
The report by Airwars, a project aimed at tracking the international air strikes targeting the militants, said it believed 57 specific strikes killed civilians and caused 48 suspected "friendly fire" deaths. It said the strikes have killed more than 15,000 Islamic State members.
While Airwars noted the difficulty of verifying information in territory held by IS, which has kidnapped and killed journalists and activists, other groups have reported similar casualties from the U.S.-led air strikes.
The group said the number of civilian casualties could exceed 591 -- far more than the two deaths acknowledged thus far by the coalition, which has only 10 active investigations of alleged civilian deaths.
U.S. State Department spokesman Mark Toner said the United States is reviewing the report's findings.
"When we receive these kinds of reliable reports, we obviously share them with the Department of Defense as well as with CENTCOM [the coalition headquarters], and we review the information rigorously," Toner said.
The United States considers it "absolutely important to protect the lives of civilians on the ground," he said.
The report said the coalition could do a much better job tracking and possibly preventing civilian deaths.
"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 United States has been conducting air strikes against IS in Iraq since last August and in Syria since September. A coalition of countries later joined to help allied ground forces combat the extremists. To date, the coalition has launched more than 5,800 air strikes in both countries.
The two civilians the United States has admitted killing in its strikes were children who were likely slain when it bombed Al-Qaeda targets in Syria last year. That same strike also wounded two adults, according to U.S. military investigation in May.
The United States has closed three investigations where it concluded allegations of civilian killings were unfounded. More investigations are pending.
U.S. 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 press reports on the additional civilian casualties but said the Pentagon will have nothing to say until the reports are reviewed.
Airwars said it identified the 57 strikes through reporting from "two or more generally credible sources, often with biographical, photographic or video evidence." The incidents also corresponded to confirmed coalition strikes conducted in the area at that time, it said.
The group is staffed by journalists and describes itself as a "collaborative, not-for-profit transparency project." It does not offer policy prescriptions.
"The coalition's war against ISIL has inevitably caused civilian casualties, certainly far more than the two deaths Centcom presently admits to," the group said.
"Yet it's also clear that in this same period, many more civilians have been killed by Syrian and Iraqi government forces, by Islamic State, and by various rebel and militia groups operating on both sides of the border."
In Iraq, the U.S.-led coalition includes France, Britain, Belgium, Netherlands, Australia, Denmark, and Canada. Jordan has also carried out air strikes in Iraq as well as in Syria.
The coalition conducting air strikes in Syria includes the United States, Saudi Arabia, Jordan, Bahrain, and the United Arab Emirates. Canada began its own strikes in April, and British pilots have carried out strikes while embedded with U.S. forces.
Airwars called for greater transparency and accountability from coalition members, since each is individually liable for any civilian deaths or injuries it causes.
"Only one of twelve coalition partners - Canada - has consistently stated in a timely fashion both where and when it carries out air strikes," the report said.
Other groups also have reported on major casualties suspected of being caused by the U.S.-led air strikes.
The Britain-based Syrian Observatory for Human Rights, which relies on a network of on-the-ground activists, said 173 Syrian civilians have been killed since air strikes began, including 53 children under the age of 18. Most of the civilians were killed in air strikes near oil refineries and oil fields in the northern provinces of Hassakeh, Raqqa, Aleppo, and Deir el-Zour.
The Observatory said the deadliest incident was on May 4, when a U.S.-led strike on the IS-controlled village of Bir Mahli killed 64 people, including 31 children. A Pentagon spokesman at the time said there was no information to indicate there were civilians in the village. The death toll was confirmed by other opposition groups in Syria.
In another incident on June 8, a strike likely conducted by the U.S.-led coalition on the IS-held village of Dali Hassan, also in northern Syria, killed a family of seven, the Observatory said.
Turkey, which recently began its own air strikes against IS targets in Syria and Kurdish militants in northern Iraq, said it would investigate accusations by the Iraqi Kurdish regional government and activists with the Kurdistan Workers' Party, or PKK, that its air strikes caused civilian casualties in the northern Iraqi town of Zargel.
The United Nations said August 3 that it is concerned about reports that 40 civilians may have been killed and over 30 wounded in an air strike west of Ramadi in Iraq's Anbar province, and called on the Iraqi government to investigate the incident.
With reporting by AP and dpa