The United States carried out large-scale military strikes on Saturday against dozens of targets in Yemen controlled by the Iranian-backed Houthi militia, President Trump announced.

It was the opening salvo in what senior American officials said was a new offensive against the militants and a strong message to Iran, as Mr. Trump seeks a nuclear deal with its government.

Air and naval strikes ordered by Mr. Trump hit radars, air defenses, and missile and drone systems in an effort to open international shipping lanes in the Red Sea that the Houthis have disrupted for months with their own attacks. At least one senior Houthi commander was targeted. The Biden administration conducted several strikes against the Houthis but largely failed to restore stability to the region.

U.S. officials said the bombardment, the most significant military action of Mr. Trump’s second term so far, was also meant to send a warning signal to Iran. Mr. Trump wants to broker a deal with Iran to prevent it from acquiring a nuclear weapon, but has left open the possibility of military action if the Iranians rebuff negotiations.

“Today, I have ordered the United States Military to launch decisive and powerful Military action against the Houthi terrorists in Yemen,” Mr. Trump said in a message on Truth Social. “They have waged an unrelenting campaign of piracy, violence, and terrorism against American, and other, ships, aircraft, and drones.”

Mr. Trump then pivoted to Iran’s rulers in Tehran: “To Iran: Support for the Houthi terrorists must end IMMEDIATELY! Do NOT threaten the American People, their President, who has received one of the largest mandates in Presidential History, or Worldwide shipping lanes. If you do, BEWARE, because America will hold you fully accountable.”

U.S. officials said that airstrikes against the Houthis’ arsenal, much of which is buried deep underground, could last for several weeks, intensifying in scope and scale depending on the militants’ reaction. U.S. intelligence agencies have struggled in the past to identify and locate the Houthi weapons systems, which the rebels produce in subterranean factories and smuggle in from Iran.

Some national security aides want to pursue an even more aggressive campaign that could lead the Houthis to essentially lose control of large parts of the country’s north, U.S. officials said. But Mr. Trump has not yet authorized that strategy, wary of entangling the United States in a Middle East conflict he pledged to avoid during his campaign.

Prime Minister Benjamin Netanyahu of Israel has been pushing Mr. Trump to authorize a joint U.S.-Israel operation to destroy Iran’s nuclear weapons facilities, taking advantage of a moment when Iran’s air defenses are exposed, after a bombing campaign from Israel in October dismantled critical military infrastructure. Mr. Trump, reluctant to be drawn into a major war, has so far held off against pressure from both Israeli and U.S. hawks to seize the opening to strike Iran’s nuclear sites.

Since the Hamas-led assault on Israel in October 2023, Houthi rebels have attacked more than 100 merchant vessels and warships in the Red Sea with hundreds of missiles, drones and speedboats loaded with explosives, disrupting global trade through one of the world’s busiest shipping lanes.

The Houthis, who are backed by Iran and act as the de facto government in much of northern Yemen, largely discontinued their attacks when Israel and Hamas reached a cease-fire in Gaza in January. But Israel instituted a blockade on aid to Gaza this month, and the Houthis have said they will step up attacks in response.

The group’s assaults in recent weeks have angered Mr. Trump. They fired a surface-to-air missile at an Air Force F-16 flying over the Red Sea, missing the jet. A U.S. military MQ-9 Reaper drone disappeared over the Red Sea the same day Houthi militants claimed to have shot one down.

“To all Houthi terrorists, YOUR TIME IS UP, AND YOUR ATTACKS MUST STOP, STARTING TODAY.” Mr. Trump said in Truth Social message.

The initial airstrikes hit buildings in neighborhoods in and around Sana, Yemen’s capital, that were known Houthi leadership strongholds, residents said. According to the Houthi-run television news channel Al Masirah, the Yemeni health ministry said that nine people had been killed and nine others injured in airstrikes. The casualties could not be independently verified.

U.S. officials said the strikes on Saturday resulted from a series of high-level White House meetings this week between Mr. Trump and top national security aides, including Vice President JD Vance; Secretary of State Marco Rubio; Michael Waltz, the president’s national security adviser; Defense Secretary Pete Hegseth; and Gen. Michael E. Kurilla, the head of the military’s Central Command. Mr. Trump approved the plan on Friday.

The strikes were carried out by fighter jets from the aircraft carrier Harry S. Truman, now in the northern Red Sea, as well as by Air Force attack planes and armed drones launched from bases in the region, U.S. officials said.

During the Biden administration, the attacks on commercial shipping were met with several counterstrikes by U.S. and British military forces. Between last January and May, for instance, the two countries’ militaries conducted at least five major joint strikes against the Houthis in response to the attacks on shipping.

United States Central Command, which carried out the strikes on Saturday without any other nation’s assistance, has regularly announced military actions against the Houthis.

But the U.S.-led strikes have failed to deter them from attacking shipping lanes connecting to the Suez Canal that are critical for global trade. Hundreds of ships have been forced to take a lengthy detour around southern Africa, driving up costs. Despite the cease-fire in Gaza, some of the biggest container shipping lines show their vessels still going around the Cape of Good Hope and avoiding the Red Sea on their websites.

The Biden administration tried to chip away at the ability of the Houthis to menace merchant ships and military vessels without killing large numbers of Houthi fighters and commanders, which could unleash even more mayhem into a widening regional war that officials feared would drag in Iran.

Fears of that broader regional conflict have greatly subsided in the months since Israel decimated Hezbollah and Hamas, two main armed proxies for Iran in the region, and destroyed much of Iran’s air defenses with a series of punishing airstrikes last fall that left the country vulnerable to an even larger Israeli counterattack should it retaliate.

That has given Mr. Trump more leeway to undertake the large-scale bombing offensive against the Houthis and use it as a warning to Iranian leaders if they balked at talks centered on Tehran’s nuclear program.

But it is unclear how a renewed bombing campaign against the Houthis would succeed where previous American-led military efforts largely failed. Military officials said these strikes would hit a broader set of Houthi targets and would be carried out over weeks. Mr. Trump did not elaborate in his message on social media.

“Joe Biden’s response was pathetically weak, so the unrestrained Houthis just kept going,” Mr. Trump said, adding: “The Houthi attack on American vessels will not be tolerated. We will use overwhelming lethal force until we have achieved our objective.”

The Houthis, whose military capabilities were honed by more than eight years of fighting against a Saudi-led coalition, have greeted the prospect of war with the United States with open delight.

The Houthis, a tribal group, have taken over much of northern Yemen since they stormed the nation’s capital, Sana, in 2014, effectively winning a war against the Saudi-led coalition that spent years trying to rout them. They have built their ideology around opposition to Israel and the United States, and often draw parallels between the American-made bombs that were used to pummel Yemen and those sent to Israel and used in Gaza.

In late January, Mr. Trump issued an executive order to redesignate Yemen’s Houthi rebels as a “foreign terrorist organization,” calling the group a threat to regional security, the White House said. Critics argued the move will worsen an already dire humanitarian crisis in the country.

The order restored a designation given to the group, formally known as Ansar Allah, late in the first Trump administration. The Biden administration lifted the designation shortly after taking office, partly to facilitate peace talks in Yemen’s civil war.

Last year, however, the Biden team reversed course, labeling the Houthis a “specially designated global terrorist” organization — a less severe category — in response to attacks against U.S. warships in the Red Sea.

Officials in Washington and the Middle East were bracing on Saturday for a Houthi counterattack.

The Houthis’ spokesman, Mohammed Abdulsalam, said on social media on Jan. 22 that supporting the Palestinian cause would remain a top priority even after the cease-fire in Gaza. The Houthis have said they would stop targeting all ships “upon the full implementation of all phases” of the cease-fire agreement.

But at the same time, the Houthis warned that if the United States or Britain directly attacked Yemen, they would resume their assaults on vessels associated with those countries. Evidence recently examined by weapons researchers shows that the rebels may have acquired new advanced technology that makes their drones more difficult to detect and helps them fly even farther.

Peter Eavis contributed reporting from New York, and Saeed Al-Batati from Al Mukalla, Yemen.