The U.S. and U.K. conducted a second round of airstrikes against Iran-backed Houthi rebels in Yemen on Monday night.

Why it matters: The strikes that the U.S. Central Command said began at 11:59pm local time come amid ongoing fears of escalation in the Middle East as the Houthis continue to attack merchant and commercial vessels in the Red Sea.

• CENTCOM said in its statement the strikes "targeted areas in Houthi-controlled Yemen used to attack international merchant vessels and U.S. Navy ships in the region."
• This is the eighth round of airstrikes the U.S. has conducted against the Houthis, per CBS News, which cited two U.S. defense officials.

State of play: The U.S. and U.K. joint airstrikes were conducted with support from Australia, Canada, Bahrain, and the Netherlands, the six countries said in a joint statement.

• The strikes were aimed at eight Houthi targets in Yemen, and aimed to disrupt and degrade the Houthis' capabilities, the statement added.
• The targets included locations associated with the rebels' missile and air surveillance capabilities as well as one of their underground storage sites, the statement added.
• The strikes were "in response to a series of illegal, dangerous, and destabilizing Houthi actions since our coalition strikes on January 11," the statement added.

U.S. Forces, Allies Conduct Joint Strikes in Yemen

As part of ongoing international efforts to respond to increased Houthi destabilizing and illegal activities in the region, on Jan. 22 at approximately 11:59 p.m. (Sanaa / Yemen time), U.S. Central Command forces alongside UK… pic.twitter.com/BQwEKZqMAo

— U.S. Central Command (@CENTCOM) January 22, 2024

What they're saying: "Our aim remains to de-escalate tensions and restore stability in the Red Sea," the countries said in the joint statement, but added that "we will not hesitate to defend lives and the free flow of commerce in one of the world's most critical waterways in the face of continued threats."

• The joint strikes were conducted in self-defense, U.K. Defense Secretary Grant Shapps said in a statement Monday.
• "Aimed at degrading Houthi capabilities this action will deal another blow to their limited stockpiles and ability to threaten global trade," he added.

The big picture: The strikes come the same day that President Biden spoke with U.K. Prime Minister Rishi Sunak over the phone about the Houthis' continued attacks on vessels in the Red Sea.

• Just last week, the Biden administration re-designated the Houthis as a "global terrorist group."
• The Houthis have conducted dozens on merchant and commercial vessels in the Red Sea since November, snarling international shipping routes.
• National Security Council spokesperson John Kirby said last week that the U.S. had "fully anticipated" that the Houthis would conduct retaliatory strikes in response to the first U.S. and U.K. airstrikes.

Go deeper: What to know about Yemen's Houthi rebels and the Red Sea conflict

Editor's note: This article has been updated with images and a statement from CENTCOM.