The US said on Friday that all six crew members in a refuelling aircraft that crashed in western Iraq have been confirmed dead.
The military initially said four had died and rescuers were searching for two others who were on board the KC-135 aircraft that crashed on Thursday.
US Central Command said the crash was being investigated, but that it was “not due to hostile fire or friendly fire”.
At least 13 American personnel have died since the US and Israel began their campaign against Iran.
According to reports, a unit of the US Marine Corps consisting of about 2,000 troops will soon head to the Middle East along with three amphibious warships.
Quoting US officials, the Wall Street Journal and ABC News reported that the 31st Marine expeditionary unit, which usually operates in the Indo-Pacific region, has been ordered to the Middle East.
The deployment does not necessarily mean that the unit will be used as a ground force in Iran, but it can offer support when needed, the reports said.
It comes after Pentagon chief Pete Hegseth said on Friday that “today” will bring the highest number of strikes on Iran since the start of the war.
“Today will be, yet again, the highest volume of strikes America has put over the skies of Iran and Tehran,” he said during a morning media briefing.
US President Donald Trump later warned Iran's “deranged” regime to expect attacks for at least another week.
He told Fox News that “we're going to be hitting them very hard over the next week”.
Mr Trump – who has sent mixed messages about the planned duration of the war – claimed the US campaign was “ahead of schedule” but suggested pressure on Iran would increase.
“We have unparalleled firepower, unlimited ammunition, and plenty of time – watch what happens to these deranged scumbags today,” he wrote on Truth Social.
“They’ve been killing innocent people all over the world for 47 years, and now I, as the 47th President of the United States of America, am killing them.”
During his briefing, Mr Hegseth said that Iranian supreme leader Mojtaba Khamenei is injured. Vice President JD Vance later echoed his comments, adding “we don't know exactly how bad”.
Mr Khamenei has succeeded his father, Ayatollah Ali Khamenei, who was killed in US-Israeli strikes earlier this month.
Mr Hegseth also said at the briefing that an investigating officer has been assigned to examine the deadly strike on a girls’ school in southern Iran.
At least 175 people, many of them children, were killed in the attack, according to Tehran. Reports have suggested the US was responsible, and a Republican senator this week called the incident a “terrible, terrible mistake”.
Centcom “has designated an investigating officer to conduct a command investigation”, Mr Hegseth said.
“The investigation will take as long as necessary to address the circumstances surrounding this incident,” he said, adding that the investigating officer is a general officer from outside Centcom
