WASHINGTON, Jan. 11 (Reuters) - The United States and Britain launched strikes from the air and sea against Houthi military targets in Yemen in response to the movement's attacks on ships in the Red Sea, a dramatic regional widening of the Israel-Hamas war in Gaza.

As witnesses in Yemen confirmed explosions throughout the country to Reuters, President Joe Biden cautioned in a statement late on Thursday he would not hesitate to take further action if needed.

"These targeted strikes are a clear message that the United States and our partners will not tolerate attacks on our personnel or allow hostile actors to imperil freedom of navigation," Biden said.

Britain's ministry of defence said in a statement that "early indications are that the Houthis' ability to threaten merchant shipping has taken a blow."

The Iran-backed Houthis say their attacks on shipping routes in the Red Sea are a show of support for the Palestinians and Hamas, the Islamist group that controls Gaza.

U.S. Defense Secretary Lloyd Austin, who is in hospital due to surgery complications, said in a statement that the strikes targeted Houthi capabilities including drones, ballistic and cruise missiles, costal radar and air surveillance.

A Houthi official confirmed "raids" in the capital Sanaa along with the cities of Saada and Dhamar as well as in Hodeidah governorate, calling them "American-Zionist-British aggression."

Witnesses told Reuters that the raids targeted a military base adjacent to Sanaa airport, a military site near Taiz airport, a Houthi naval base in Hodeidah and military sites in Hajjah governorate.

Photo from Reuters