WASHINGTON, D.C.: American forces targeted 14 missiles that were ready to launch in Yemen, the United States military said on Wednesday, after Washington redesignated the Iran-backed Houthi rebels as a "terrorist" entity for their attacks on merchant vessels.

The Houthis — who have already faced multiple rounds of airstrikes in response to their targeting of commercial ships — struck a US-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.

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

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

Hani Kayed, a 44-year-old resident of the Yemeni port city of Hodeida, told Agence France-Presse (AFP) he heard an explosion at about 2:16 a.m. (local time) in the city's east, near the airport.

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

The US announced earlier on 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," US Secretary of State Antony Blinken said in a statement.

"During the 30-day implementation delay, the US 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 added.

US-owned ship targeted

In a statement, US national security adviser 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," he added.

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, saying they would respond to new strikes on Yemen by the US or UK.

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 spokesman Yahya Saree said in televised remarks that they targeted a US vessel called the Genco Picardy in the Gulf of Aden.

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

"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" redesignation 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.