Donald Trump’s press secretary Sean Spicer falsely accused Iran of attacking a United States naval vessel, an incident which - if it had really happened - could constitute an act of war.

Mr Spicer made the remarks during a press briefing called to explain a White House announcement that Iran had been officially "put on notice”, following a ballistic missile test and an attack on a Saudi naval vessel by suspected Houthi rebels off the coast of Yemen.

The President's spokesman appeared to both conflate Iran with the Houthis, a militia fighting the Saudi-backed Yemeni government, and confuse the US with Saudi Arabia in his comments.

“I think General Flynn was really clear yesterday that Iran has violated the Joint Resolution, that Iran’s additional hostile actions that it took against our Navy vessel are ones that we are very clear are not going to sit by and take,” he said.

Major Garrett, Chief White House Correspondent with CBS News, can then be heard in video of the briefing quietly correcting him — “a Saudi vessel” — to which Mr Spicer responded: “Sorry, thank you, yes a Saudi vessel. Yes, that’s right.”

The press secretary did not correct the allegation that the Iranian government carried out the attack.

Fox News had initially reported — incorrectly — that a US vessel was the target of the attack, which may have contributed to Mr Spicer's apparent confusion, but the Pentagon later confirmed it was a Saudi ship attacked by a group speculatively identified as Houthi.

The Intercept noted that although Mr Spicer's mix up is easy to ridicule, it could have grave consequences — in the past alleged attacks on US forces that did not actually happen have resulted in military retaliation, including during the Vietnam war.

The US has had ships in the Gulf area since former President Barack Obama's administration dispatched vessels to the Bab-el Mandeb strait off the coast of Yemen in October, to reinforce a Saudi-led naval blockade that contributed to the country's ongoing food crisis.

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Iran also has a presence in the area, were it is backing the Houthi insurgency, including by supplying the group with weapons.

Last weekend, Mr Trump authorised a raid on a branch of al-Qaeda in Yemen — his first military operation as commander in chief — in which medics at the scene said about 30 people, including 10 women and children, were killed.

Navy SEAL William “Ryan” Owens also died in the raid in al Bayda province, along with 14 militants, according to the Pentagon.