(CNN) — The US on Saturday conducted strikes against Houthi anti-ship cruise missiles and vessels, including on the first unmanned underwater vessel the Iranian-backed rebel group has used since the attacks in the Red Sea began, according to US Central Command.

The US conducted five strikes against three anti-ship cruise missiles, one unmanned underwater vessel and one unmanned surface vessel between 3 and 8 p.m. Saturday local time, CENTCOM said.

“CENTCOM identified the anti-ship cruise missiles, unmanned underwater vessel, and the unmanned surface vessel in Houthi-controlled areas of Yemen and determined they presented an imminent threat to U.S. Navy ships and merchant vessels in the region,” Central Command said in a statement Sunday.

The unmanned underwater vessel attack marks a new strategy for the Houthis and comes in spite of continued US airstrikes against the rebel group. Earlier this month, the US and UK struck at least 30 Houthi targets across at least 10 locations in Yemen with the aim to “de-escalate tensions and restore stability in the Red Sea.”

The Houthis have been attacking US targets and commercial shipping in the Red Sea since Israel launched its invasion of Gaza following Hamas’ October 7 attack. There are fears that the attacks could escalate Israel’s war against Hamas into a wider regional conflict.

The Houthi attacks have forced some of the world’s biggest shipping and oil companies to suspend transit through one of the most important maritime trade routes, which could potentially cause a shock to the global economy.

CNN last week was on board two vessels spearheading the US response to Houthi attacks in the southern Red Sea as the Navy works at a frenetic pace deploying jets and firing missiles at a moment’s notice to try to destroy the Houthis’ weapons and infrastructure.

This story has been updated with additional information.

CNN’s Jack Forrest, Natasha Bertrand, Oren Liebermann, Haley Britzky and Christian Edwards.