The strikes occurred on 3 pm and 8 pm Sanaa time (1200 and 1700 GMT), the US military said, and are part of a series of actions taken by the United States and its allies against the Huthis, aimed at halting the Iran-backed rebels' repeated attacks on Red Sea shipping lanes.

The five strikes included targeting "the first observed Huthi employment of a UUV (unmanned underwater vessel) since attacks began" in October, according to a statement from the US Central Command.

Another of the five involved an unmanned surface vessel, or USV, essentially a floating drone. The use of such vessels has been comparatively rare.

The other three involved anti-ship cruise missiles, the statement said.

"CENTCOM identified the anti-ship cruise missiles, unmanned underwater vessel, and the unmanned surface vessel in Huthi-controlled areas of Yemen and determined they presented an imminent threat to US Navy ships and merchant vessels in the region," it said, adding that it struck the five to "make international waters safer."

The Huthis, who control much of war-torn Yemen including the port of Hodeida, began their attacks in November, saying they were hitting Israel-linked vessels in support of Palestinians in Gaza, which has been ravaged by the Israel-Hamas war.

US and British forces have responded with strikes against the Huthis, who have since declared the two countries' interests to be legitimate targets as well.

The Red Sea attacks have raised insurance premiums for shipping companies, forcing many to avoid the Red Sea, a vital route that normally carries about 12 percent of global maritime trade.