“Tonight the U.S. military, in coordination with our partners, conducted strikes in Houthi-controlled areas in Yemen,” the Pentagon said in a brief statement. “We will have more details to share soon.”

Senior U.S. officials have blamed Iran for having “aided and abetted” the crisis in the Red Sea, saying the Houthis would be incapable of threatening the shipping route if not for Tehran’s technological and intelligence support.

Thursday’s strikes will almost certainly heighten tensions across the Middle East, which has seen widening violence since Hamas, another entity aligned with Iran, carried out a stunning cross-border attack on Israel in October. The ensuing war in Gaza has left the Biden administration deeply worried that a strong military response to the Houthis would invite further escalation by Tehran.

Iran-backed militias in Iraq and Syria have stepped up their targeting of U.S. forces deployed in both countries. American troops have absorbed at least 131 attacks since Oct. 17, according to Pentagon data. The U.S. administration has retaliated with occasional airstrikes, including last week’s killing of a militia leader in Baghdad, but it had up to now withheld a forceful response against the Houthis.

An incident Tuesday marked a turning point, officials said. U.S. and British forces shot down 18 one-way attack drones, two cruise missiles and one ballistic missile that had been launched as dozens of merchant ships moved through the Red Sea, according to U.S. Central Command. The onslaught was repulsed by a combination of warships and fighter jets.

A U.S. official, speaking on the condition of anonymity due to the issue’s sensitivity, characterized the encounter as complex and brazen.

“These attacks are a threat to international norms, U.S. interests, and maritime trade. Their actions defy international law and destabilize the region, benefiting no one,” the official said.

Thursday’s operation was preceded by a statement, signed by 13 countries, demanding the Houthis cease their attacks or be held accountable.

At a moment when its strong support for Israel’s campaign against Hamas has put the United States at odds with numerous global partners, the Biden administration has attempted to enlist allied nations in intensifying pressure on the Houthis and to frame that effort as an international campaign.

While the United States conducted a years-long air campaign against al Qaeda militants in Yemen, it has mostly avoided military action against the Houthis, who took power in the capital Sanaa in late 2014. The U.S. Navy did launch missiles at radar sites in Yemen in 2016 following missile attacks on American vessels.

The Houthi takeover ignited a prolonged civil war in Yemen that eventually drew in forces from Saudi Arabia and the United Arab Emirates and took a grisly toll on Yemeni civilians. U.S. and U.N. officials have conducted a years-long diplomatic effort to halt that conflict but have been unable to broker a political agreement between the warring Yemeni parties.

The violence has subsided substantially since a ceasefire, now expired, took effect in 2022.

Rep. Elissa Slotkin (D-Mich.), vice chair of the House Armed Services intelligence and special operations subcommittee, said the volume and complexity of Houthi activity “has made very clear to me that we need to reestablish deterrence.” That is done, she added, “by striking back at them, and you do it in a precision way, and we do everything we can to minimize civilian casualties.”

Some analysts were doubtful the operation would have the intended effect of curbing the Red Sea attacks.

“The Houthis win by taking a U.S. strike, no matter how heavy, and showing that they can keep going with the shipping attacks,” said Michael Knights, a scholar at the Washington Institute for Near East Policy. “The Houthis are high on their successes and will not be easy to deter. They are having the time of their lives, standing up to a superpower who probably cannot deter them.”

Others have said a strong response was necessary. Kenneth “Frank” McKenzie, a retired general who led U.S. Central Command before retiring in 2022, said earlier this week that it was important to inflict “pain” on the militants responsible.

“And that means you’ve got to strike targets in Yemen that are important to the Houthis,” he said.

The Biden administration’s effort to build an international consensus against the Houthi violence was strengthened Wednesday when the United Nations Security Council passed a resolution voicing strong condemnation of the attacks. The resolution, which was sponsored by the United States and Japan, was approved 11 in favor and zero against, with abstentions by Russia, China, Algeria and Mozambique.

Tehran itself also has pursued aggressive action. Earlier Thursday, the Iranian navy seized a Marshall Islands-flagged oil tanker in the Gulf of Oman while it was en route to Turkey, the U.S. Navy said. The crew’s status is unknown. Iran now holds five ships and 90 crew members “hostage,” officials said.