The United States began to carry out large-scale military strikes on Saturday against dozens of targets in Yemen controlled by the Iranian-backed Houthi militia, according to local news reports and two senior U.S. officials, the opening salvo in what American officials said was a new offensive against the militants.

Air and naval strikes ordered by President 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. The Biden administration conducted several similar strikes against the Houthis but largely failed to restore deterrence in the region.

U.S. officials said the bombardment, the most significant military action of Mr. Trump’s second term, 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.

U.S. officials said that airstrikes against the Houthis’ arsenal, much of which is buried deep underground, could last for several days, 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 would 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.