A US plane was lost during military operations against Iran.
US Central Command has confirmed the KC-135 refuelling aircraft in friendly airspace over western Iraq.
A Washington spokesman confirmed the plane was not lost due to friendly or hostile fire.
The spokesman said the officials were working to gather additional details and provide clarity for the families of service members.
A spokesman said: "US Central Command is aware of the loss of a US KC-135 refueling aircraft.
"The incident occurred in friendly airspace during Operation Epic Fury, and rescue efforts are ongoing. Two aircraft were involved in the incident. One of the aircraft went down in western Iraq, and the second landed safely.
"This was not due to hostile fire or friendly fire.
"More information will be made available as the situation develops. We ask for continued patience to gather additional details and provide clarity for the families of service members."
The KC-135 refueling aircraft was lost (file pic)
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Since the US and Israel started carrying out strikes against Iran on February 28, seven US troops have been killed.
Reuters reported on Tuesday that as many as 150 US troops have been wounded in the US-Israeli war on Iran.
The latest death toll reported by state media on Monday was at least 1,270 people.
However, Iran's ambassador to the United Nations said on March 6 that at least 1,332 people had been killed since the war began. There has been no clarification of the discrepancy.
It was not clear if those figures include at least 104 people that the Iranian military said were killed in a US attack on an Iranian warship off Sri Lanka's coast on March 4.
Smoke and flames rise at the site of airstrikes on an oil depot in Tehran
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In Lebanon, at least 687 people have been killed in Israeli strikes, according to Lebanese authorities. The World Health Organization said at least 98 of those killed were children.
At least 30 people have been killed in Iraq, according to local health authorities. Most of those were members of the Shi'ite Popular Mobilisation Forces.
In Israel, 12 people have been killed, including nine people in an Iranian missile strike on Beit Shemesh near Jerusalem on March 1, according to Israel's ambulance service Magen David Adom.
The military said two soldiers were killed in southern Lebanon, the first fatalities among its troops since hostilities with Hezbollah resumed last week.
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Missiles launched from Iran in retaliation for Israeli attacks are seen in the night sky over the city of Hebron in the West Bank
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Israeli Prime Minister Benjamin Netanyahu said Iran was "no longer the sam"e after nearly two weeks of joint U.S.-Israeli attacks and had suffered blows to its elite forces.
Appearing in his first press conference since the start of the war, Netanyahu said he spoke with President Donald Trump nearly every day and that the two men spoke "openly" about the war.