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Aboard the USS Kearsarge • The U.S. airstrike that may have killed a number of Iraqi soldiers Friday seems to be "a mistake that involved both sides," U.S. Defense Secretary Ash Carter said Saturday. Iraq pledged to punish those responsible.

Speaking to reporters during a visit to the USS Kearsarge in the Persian Gulf, Carter said the incident near the western Iraqi city of Fallujah was "regrettable." He called Iraqi Prime Minister Haider al-Abadi to express condolences.

"These kinds of things happen when you're fighting side by side as we are," Carter said. He said the airstrike "has all the indications of being a mistake of the kind that can happen on a dynamic battlefield."

Iraqi Defense Minister Khalid al-Obeidi told reporters in Baghdad that the strike killed one officer and nine soldiers. He said Iraq had begun an investigation and that the "wrongdoer would be punished according to Iraqi law." He did not elaborate. He said he would "not neglect the blood of Iraqis."

Carter, who spent two days in Iraq this past week, called Abadi from the USS Kearsarge, an amphibious assault ship supporting coalition missions in Iraq and Syria against Islamic State militants.

The Kearsarge carries a Marine expeditionary unit and naval aircraft.

The Pentagon chief did not provide details about the airstrike, which the U.S. military headquarters in charge of the war effort in Syria and Iraq said was one of several it conducted Friday against Islamic State targets.

The U.S. military statement said the airstrikes came in response to requests and information provided by Iraqi security forces on the ground near Fallujah, which is in Islamic State control, and were done in coordination with Iraqi forces.

A senior U.S. defense official said there was fog in that area and that weather may have played a role in the incident. "The coalition is investigating the incident and will make further details available when appropriate."

Carter said he told Abadi that the United States was investigating and would work with the Iraqis.

Asked if he was worried the deaths might further anger Iraqi citizens who may not be happy with the American and coalition presence in Iraq, Carter said, "I hope Iraqis will understand that this is a reflection of things that happen in combat. But it's also a reflection of how closely we are working with the government" of Iraq.

He added that during the call, both he and Abadi recognized that "things like this can happen in war."

The Iraqi government is under pressure from parliament to deliver a strong response.

The parliamentary Defense and Security Committee said it was demanding a "tough stance" from Iraq's leadership. Lawmaker Mohammed al-Karbouli said the "repetitive targeting" of Iraqi forces "raises suspicions over the credibility" of the U.S.-led coalition fighting the Islamic State.

Carter met with Abadi during a stop in Baghdad on Monday to discuss the fight against the Islamic State, and the U.S. plans to accelerate the campaign.