The U.S. military’s surprise strikes on Yemen’s Houthi militants over the weekend continued into Monday after Defense Secretary Pete Hegseth pledged an “unrelenting” campaign until the group stops attacking vessels in the Red Sea.

“This campaign is about freedom of navigation and restoring deterrence. The minute the Houthis say, ‘We’ll stop shooting at your ships, we’ll stop shooting at your drones,’ this campaign will end,” Hegseth said in an interview on Fox News’s “Sunday Morning Futures,” a day after President Trump ordered the strikes. 

“But until then, it will be unrelenting.”

President Trump ordered the strikes on Houthi targets on Saturday, promising to use “overwhelming lethal force” until the Iran-backed group stopped their attacks on civilian and military ships in the vital maritime corridor. 

He also has warned Iran to stop supporting the Houthis, declaring that the country will be held directly responsible for any future attacks by the rebel group. 

But the Houthis have responded that they will not be deterred by the U.S. airstrikes and would retaliate for the latest U.S. attacks. 

Here’s what to know about the operation:

Shortly after 1 p.m. Saturday, Air Force attack jets and armed drones took off from various bases in the region, along with fighter planes from the USS Harry S. Truman aircraft carrier, to strike targets in Yemen’s capital of Sana’a, the Saada province to the north and Dhamar and Al Bayda provinces to the south.

Saada is the Houthis’ stronghold on the border with Saudi Arabia, while Sana’a holds Houthi military facilities and the headquarters of their political bureau.

On Sunday, the Houthis also reported airstrikes on the provinces of Hodeida, Bayda and Marib.

The Houthis say at least 53 people have been killed in the strikes and more than 100 injured, the majority women and children, according to the Houthi-run Saba News Agency.

U.S. officials said the initial wave of strikes hit more than 30 targets at multiple locations on Saturday, including terrorist training sites, unmanned aerial vehicle infrastructure, weapons manufacturing capabilities and weapons storage facilities. 

“It also included a number of command and control centers, including a terrorist compound where we know several senior Houthi unmanned aerial vehicle experts were located,” Lt. Gen. Alexus Grynkewich, joint staff director for operations, told reporters Monday.

The U.S. strikes continued on Sunday against additional headquarters locations, weapon storage facilities, and what Grynkewich said were Houthi detection capabilities that have been used to threaten maritime shipping in the past. 

“Today, the operation continues, and it will continue in the coming days until we achieve the president’s objectives,” he said, noting that the Pentagon has assessed that the strikes have taken out “dozens” of Houthi rebels.  

White House national security adviser Mike Waltz told Fox News on Sunday the attacks “hit the Houthi leadership, killing several of their key leaders last night, their infrastructure, the missiles.”

The airstrikes come days after the Houthis declared they would resume attacks on Israeli vessels sailing off Yemen, a response to Israel’s blockade of aid to the war-torn Gaza Strip earlier this month. 

Israeli ships passing through the Arabian and Red seas, the Gulf of Aden and Bab el-Mandeb Strait were warned by the rebel group that they will become a target “until the crossings to the Gaza Strip are reopened and aid, food, and medicine are allowed in.” 

Houthi spokesperson Nasr el-Din Amer told NBC News that the group plans to retaliate for the weekend attacks and would not stop until the “blockade on Gaza” is lifted.

“We will respond to the recent escalation with further escalation,” he said.

The strikes come after Trump in late January signed an executive order that recognized the Houthis in Yemen as a foreign terrorist organization.

Trump said Saturday on Truth Social the aerial attacks were meant to “protect American shipping, air, and naval assets, and to restore Navigational Freedom.” 

He added the Houthis have “choked off shipping in one of the most important Waterways of the World, grinding vast swaths of Global Commerce to a halt.” 

Since the war in Gaza began in late 2023, the Houthis have targeted more than 100 merchant and military vessels with missiles and drone strikes. The attacks sank two ships, killed four sailors and upended a vital international shipping route.  

The Biden administration had attempted to deter the attacks with their own missile strikes against the Houthis. But the Trump administration has said a larger, more extended campaign against the Houthis is needed. 

Pentagon press secretary Sean Parnell told reporters Monday the U.S. will use “overwhelming lethal force until we have achieved our objective,” but he stressed that the strikes are “not an endless offensive.” 

Trump on Monday vowed to hold Iran responsible for any future shots fired by the Houthis, pledging that any attack or retaliation by the rebel group “will be met with great force, and there is no guarantee that that force will stop there.”

Iran is “dictating every move, giving them the weapons, supplying them with money and highly sophisticated Military equipment, and even, so-called, ‘Intelligence.’ Every shot fired by the Houthis will be looked upon, from this point forward, as being a shot fired from the weapons and leadership of IRAN, and IRAN will be held responsible, and suffer the consequences, and those consequences will be dire!” Trump wrote on Truth Social.

White House press secretary Karoline Leavitt later doubled down on Trump’s threat to Tehran, saying the U.S. message to the country is “you better take this president seriously.”

“This president is not just going to sit on his hands and allow terrorists to launch attacks on commercial vessels and U.S. Navy ships. Those actions will not be tolerated,” she said.