WASHINGTON (AP) — An American military refueling plane went down in Iraq and rescue efforts were underway, U.S. Central Command said Thursday.

The KC-135 aircraft was part of the operation against Iran, but the crash was not due to hostile fire or friendly fire, the military said in a statement.

U.S. Central Command, which oversees the Middle East, said that two aircraft were involved and that one landed safely and the other went down in western Iraq. It described the latter as “a loss.”

A U.S. official, who spoke on condition of anonymity to discuss a developing situation, said the other plane involved also was a KC-135 tanker.

“More information will be made available as the situation develops,” Central Command said in a statement. “We ask for continued patience to gather additional details and provide clarity for the families of service members.”

The tanker is the fourth publicly acknowledged aircraft to crash as part of the U.S. military’s operations against Iran. Last week, the military confirmed that three American fighter jets were mistakenly downed by friendly Kuwaiti fire.

All six crew members safely ejected from the F-15E Strike Eagles and were in stable condition after being recovered, the U.S. said.

Seven American troops have been killed in combat during the Iran war so far. About 140 U.S. service members have been wounded, including eight severely, the Pentagon said earlier this week.