The U.S. military launched Wednesday fresh strikes on Houthi targets after redesignating the group as terrorists and an attack on a second U.S.-operated vessel in the Red Sea region.

The Houthis – who have already faced multiple rounds of airstrikes in response to their targeting of international shipping – struck a U.S.-owned bulk cargo carrier in the wake of the designation announcement, and vowed to continue attacks they say are in support of Palestinians in Gaza.

U.S. forces "conducted strikes on 14 Iran-backed Houthi missiles that were loaded to be fired in Houthi-controlled areas in Yemen," Central Command (CENTCOM) said in a statement.

"These missiles on launch rails presented an imminent threat to merchant vessels and U.S. Navy ships in the region and could have been fired at any time, prompting U.S. forces to exercise their inherent right and obligation to defend themselves," CENTCOM said.

Hani Kayed, a 44-year-old resident of the Yemeni port city of Hodeida, told AFP he heard an explosion at around 2:16 a.m. (11:16 p.m. GMT Wednesday) in the east of the city near the airport.

Hodeida and the city of Taez were among the targets of the first round of U.S. and U.K. strikes in Yemen last week. Houthi media outlet Al-Masirah TV said both were hit again in the latest strikes, along with three other areas.

The United States announced earlier Wednesday that it would return the Houthis to a list of "terrorist" entities.

"The Department of State today is announcing the designation of Ansarallah, commonly referred to as the Houthis, as a Specially Designated Global Terrorist group, effective 30 days from today," Secretary of State Antony Blinken said in a statement.

"During the 30-day implementation delay, the U.S. government will conduct robust outreach to stakeholders, aid providers, and partners who are crucial to facilitating humanitarian assistance and the commercial import of critical commodities in Yemen," he said.

US-owned ship targeted

U.S. National Security Advisor Jake Sullivan said the designation "is an important tool to impede terrorist funding to the Houthis, further restrict their access to financial markets, and hold them accountable for their actions."

"If the Houthis cease their attacks in the Red Sea and Gulf of Aden, the United States will immediately reevaluate this designation," Sullivan said in a statement.

The Houthis, however, said they would not call off their strikes.

"We will not give up targeting Israeli ships or ships heading toward ports in occupied Palestine ... in support of the Palestinian people," the group's spokesman Mohammed Abdelsalam told Al Jazeera TV, adding that they would respond to new strikes on Yemen by the United States or Britain.

While the Houthis say they have been attacking Israeli-linked vessels, Washington says dozens of countries have connections to the ships that have been targeted in the vital waterway.

The rebels have also declared American and British interests "legitimate targets," and Houthi military spokesperson Yahya Saree said in televised remarks that they targeted a U.S. vessel called the Genco Picardy in the Gulf of Aden.

CENTCOM confirmed the vessel had been targeted Wednesday, saying a drone was launched from Houthi-controlled territory in Yemen and hit the U.S.-owned and -operated, Marshall Islands-flagged bulk carrier ship.

Military, diplomatic pressure

There were no injuries and some damage reported. M/V Genco Picardy is seaworthy and continuing underway," CENTCOM said in a social media post.

The "terrorist" designation is part of Washington's strategy to put pressure on the Houthis, which also includes military action and the establishment of an international coalition to help protect shipping from the rebels' attacks.

On Tuesday, the U.S. military said it destroyed four anti-ship missiles in Yemen that posed an imminent threat to military and civilian vessels.

The United States and Britain targeted nearly 30 sites in Yemen with more than 150 munitions last week, while U.S. forces later attacked a Houthi radar site in what was described as "a follow-on action" to the previous strikes.

In 2021, U.S. President Joe Biden's administration removed his predecessor Donald Trump's last-minute designation of the Houthis as both a foreign terrorist organization and a specially designated global terrorist group.

The removals came in response to fears from aid groups that they would need to pull out of Yemen because they are obliged to deal with the rebels, who effectively are the government in vast areas including the capital Sanaa.

The United States decided to use the specially designated global terrorist designation now because it "provides better flexibility to achieve the aims that we have in terms of carving out and safeguarding humanitarian assistance, as well as the broader well-being of the people of Yemen," a senior administration official said.