US President Joe Biden on Friday called Yemen’s Houthi forces a “terrorist” group, after American and British warplanes, ships and submarines launched dozens of air strikes across Yemen overnight.

Biden said Washington would respond to the Houthis if they continued behaviour that he called “outrageous.”

London and Washington say their strikes in Yemen were in retaliation for months of attacks by the movement on Red Sea shipping that the Iran-backed fighters cast as a response to the ongoing war in Gaza.

The strikes represent one of the most dramatic demonstrations to date of the widening of the Gaza conflict.

“I think they are,” Biden told reporters on Friday when he was asked if he was willing to call the Houthis a “terrorist” group.

“We will make sure that we respond to the Houthis if they continue this outrageous behavior along with our allies,” he added.

Biden said he was concerned about the impact of war in West Asia on oil prices, which rose on Friday.

“I am very concerned,” Biden told reporters on Friday when asked how concerned he was about the impact of the strikes in Yemen on oil prices, suggesting that impact was a key reason why the conflict should be stopped from widening.

“That’s why we got to stop it.”

The White House said earlier on Friday the US does not want war with Yemen but will not hesitate to take further action.