Two other service men were wounded in the April 24 attack, which saw a US coalition aircraft strike Iraqi Federal Police forces near al-Dib in Kirkuk province.
"Wounded are in stable condition and receiving medical care. The incident is under investigation," the spokesperson added.
Iraq's Ministry of Defence said in a statement it was opening its own investigation into casualties caused by a coalition airstrike in northern Iraq.
Early last year, US-led coalition fire killed 10 members of the Iraqi security forces and a local official in an air strike west of Baghdad, according to a Reuters report.
Coalition spokesperson at the time, Colonel Ryan Dillon, tweeted that all air strikes are carried out either at the request or with the approval of Iraqi forces.
US forces left Iraq in 2011, only to return in 2014, at the head of the coalition against IS in Iraq and Syria.
After the defeat of the Islamic State in Iraq, there have been growing domestic calls for US troops to withdraw from the country, particularly by groups politically aligned with neighbouring Iran.
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