Eight U.S. Marines were injured Sept. 14 when an Iranian anti-ship cruise missile struck the vessel they were operating on in the Strait of Hormuz, three U.S. officials told NBC News, in an attack the Pentagon had not disclosed.
The Marines suffered smoke inhalation and possible traumatic brain injuries, with concussion-like symptoms such as headaches, but were not seriously hurt and soon returned to duty, the officials said.
The Defense Department did not disclose any Sept. 14 attacks on U.S. forces in the region.
The report adds to growing scrutiny over how the Pentagon tracks and reports casualties in the war with Iran, which began in February.
Seven of the Marines were enlisted personnel, and one was an officer, according to the officials. They were operating as part of a battalion landing team during the attack.
The vessel was not a U.S. Navy ship, the officials said.
They declined to specify its type, describing it only as a maritime vessel.
The Pentagon's Defense Casualty Analysis System (DCAS) listed 861 U.S. service members as injured in the war with Iran. The eight Marines were added nearly 10 days after the attack, without details on where, when or how they were hurt.
One official attributed the delay to symptoms not always being reported immediately and to the system not updating in real time.
Reporting on U.S. casualties has been inconsistent during the war, noting that the Pentagon lowered its count of the dead over the summer after reclassifying how some troops were killed.
More than 50,000 U.S. service members are deployed across the U.S. Central Command (CENTCOM) area, including two carrier strike groups led by the USS George Washington and USS George H.W. Bush.
The U.S. continues to enforce a naval blockade on ships entering or leaving Iranian ports while coordinating safe passage for commercial vessels, shooting down Iranian projectiles and clearing mines from traffic lanes.
Iran's Islamic Revolutionary Guard Corps (IRGC) still attempts to attack ships nearly every day, one official said.
Iran has not commented on the attack that injured the U.S. Marines.