The United States has re-designated the Houthi rebels in Yemen as global terrorists in response to the group's attacks on ships around the Red Sea. But the attacks continued even after the designation.

The US government on Wednesday put the Houthis back on its list of "specially designated global terrorist" groups. The move will allow the US government to impose sanctions, such as freezing assets, on Houthi members and their supporters.

White House National Security Council spokesperson John Kirby told reporters the Houthi attacks are a clear violation of international law and are a major threat to innocent lives and global commerce. Kirby said if the Houthis do not stop the attacks, the US will not hesitate to take further action.

About two hours after the designation was announced, the Houthis attacked a US-owned cargo ship off Yemen.

The US Central Command said a drone launched from Houthi-controlled areas in Yemen struck the vessel in the Gulf of Aden. It said there were no injuries, but some damage was reported.

Meanwhile, the US Central Command also said its forces conducted strikes on Houthi missiles that were loaded to be fired.

It said the missiles presented an imminent threat to merchant vessels and US Navy ships in the region and prompted US forces to exercise their right to defend themselves.

The Central Command said the strikes will degrade the rebel group's capabilities to continue their reckless attacks on international and commercial shipping.

US media reports say this was the fourth time in days the US military has conducted strikes on Houthi positions.