Six troops died on Sunday when an unmanned aerial system penetrated air defences and struck a command centre at Port Shuaiba in Kuwait. initially reported three fatalities, but officials said on Monday that the toll rose to six after one service member died of injuries and two additional bodies were recovered from the rubble.

They are the only US fatalities confirmed since Washington entered the conflict alongside Israel.

On Tuesday, the military named four of the dead — all members of the US Army Reserve: Capt Cody Khork, 35; Sgt Noah Tietjens, 42; Sgt Nicole Amor, 39; and Sgt Declan Coady, 20.

Khork, from Florida, had previously deployed to Saudi Arabia, Guantanamo Bay and Poland. Amor, a Minnesota native, had served in Kuwait and Iraq. Tietjens, from Nebraska, had completed two earlier deployments to Kuwait. All three had received military decorations.

Coady, an Iowa resident, was posthumously promoted from specialist. He had joined the Army Reserve three years ago.

Speaking on Monday, Defence Secretary said a “powerful weapon” hit a “fortified tactical operations centre.” However, three US officials familiar with the incident told CBS News that the personnel had been working in a makeshift office — a trailer shielded by 12-foot (3.7m) steel-reinforced concrete barriers — and questioned whether the site was adequately protected.

The United States maintains a longstanding defence partnership with Kuwait and stations more than 13,000 troops in the Gulf state.

In response to attacks against it, Iran has launched missiles at Gulf countries allied with Washington. Bahrain, the United Arab Emirates, Saudi Arabia, Oman and Qatar have all reported strikes.

In a separate incident in Kuwait on Monday, the US confirmed that three fighter jets were lost in what it described as “friendly fire.” Video footage showed the aircraft spiralling to the ground, though all pilots ejected safely and survived.

Iranian state media claimed its forces had shot down the jets but provided no evidence to support the assertion.