The Iran-backed Houthis in Yemen have vowed retaliation for attacks led by the United States and U.K. in Yemen.

The strikes killed at least five Houthi fighters, NBC News reported. The attacks in Yemen were carried out from land and sea, and targeted more than 60 targets at 16 locations.

President Joe Biden said he had ordered the strikes, according to CNN.

“Today, at my direction, U.S. military forces — together with the United Kingdom and with support from Australia, Bahrain, Canada, and the Netherlands — successfully conducted strikes against a number of targets in Yemen used by Houthi rebels to endanger freedom of navigation in one of the world’s most vital waterways,” the president said in a White House statement.

Preparations for an attack on Houthis followed a United Nations Security Council resolution on Wednesday for an “immediate” end to Houthis attacks in the Red Sea, per BBC.

Report: U.S., U.K. ‘poised’ to attack Yemen’s Houthis

Why did the U.S. and other countries strike Yemen?

Yemen’s Houthis began attacking ships in the Red Sea in response to the Hamas-Israel war after the Oct. 7 Hamas attack on Israel. The attacks have affected major shipping routes and freight rates.

The “most brazen” Houthi attack yet happened Tuesday, according to Politico. After that, Biden “decided it was time to move forward” on a military response following weeks of trying to pursue other options.

What’s happening in the Red Sea?
Who are Yemen’s Houthis?

Biden said the attacks on Yemen show that the U.S. and allies “will not tolerate” the Houthis’ Red Sea attacks, The Associated Press reported.

“I will not hesitate to direct further measures to protect our people and the free flow of international commerce as necessary,” Biden’s statement read.

What’s next?

Biden and U.S. allies tried to avoid a military response in fears it would threaten an “expansion of the conflict in the Middle East beyond Israel’s war in Gaza,” according to NBC News.

U.S. officials said they haven’t yet seen a Houthi response, but they’re prepared for one, Politico reported.

Biden administration officials believe Houthi Red Sea attacks will continue, a prospect that could potentially “bind” Biden to more military action, according to CNN.