Who are the Houthis and why did the US and UK retaliate for attacks?

The U.S. had prior concerns about upending a shaky truce in Yemen and triggering a wider conflict in the Middle East.

When U.S. and U.K. warships and aircraft launched waves of missiles at Iranian-backed Houthi rebels in Yemen early Friday in Sanaa, it capped weeks of warnings to the group to cease their drone and missile attacks against commercial vessels in the Red Sea or face severe consequences.

Previously the U.S. had withheld striking back, reflecting larger U.S. concerns about upending the shaky truce in Yemen and triggering a wider conflict in the region. But on Tuesday, the Houthis launched their largest-ever barrage of 18 one-way attack drones, anti-ship cruise missiles and an anti-ship ballistic missile at a host of international commercial vessels and warships in the Red Sea.

While the U.S. and partner military ships and aircraft now protecting the waterways were able to deflect Tuesday's attack, the scope and severity of the launch drew international condemnation and left few options other than to carry through with international warnings that any further attacks would draw a substantial response.

In response, the U.S. and U.K. struck Houthi missile, radar and drone capabilities to degrade the group's ability to conduct more attacks like Tuesday's barrage.

In response to the strikes, which occurred in Yemen just before Friday 3 a.m. local time, the rebel group has already pledged to retaliate. Later in the day, the Houthis said the strikes killed five of their forces and wounded six.