It was the first time U.S. forces observed the Iranian-backed rebel group using what the military called an “unmanned underwater vessel” — or UUV — since beginning a spate of attacks in the region on Oct. 23, officials added.

Houthi rebels have been going after international commercial vessels passing through the Red Sea in recent months. The group’s leaders claim they’re targeting ships with links to Israel in response to the country’s ongoing invasion of Gaza. Many of the targeted ships have no connection to Israel.

Houthis promise to respond to U.S. and U.K. strike in the Red Sea

A powerful rebel group backed by Iran, the Houthis voice support for Hamas and have been in control of large parts of Yemen — including the capital Sanaa — since overthrowing the country’s government in 2014.

Rebels have fired missiles at and deployed drones against commercial vessels traveling through the area, and the U.S. military has repeatedly stepped in to help repel the attacks. Houthi attacks have also targeted U.S. warships.

Last month, the U.S., along with the United Kingdom and other allies, began a series of retaliatory strikes against dozens of Houthi targets in Yemen.

U.S. officials said at the time that more than 2,000 ships have had to divert course to avoid transiting the Red Sea, potentially contributing to global shipping delays.

U.S. Central Command said that on Saturday between 3:00 p.m. and 8:00 p.m. Sanaa time it successfully conducted five “self-defense strikes” against the UUV, an unmanned surface vessel and three mobile anti-ship cruise missiles.

The military said it identified the attacks in Houthi-controlled areas of Yemen and determined that they “presented an imminent threat to U.S. Navy ships and merchant vessels in the region.”