White House had reversed designation against rebel group in 2021 to help get aid to war-torn Yemen.

The White House says it is considering redesignating Yemen’s Houthi rebels as a “terrorist” group after they claimed the seizure of a commercial ship in the Red Sea.

United States National Security Council spokesperson John Kirby on Tuesday condemned the seizure, calling it the “piracy of a ship in international waters”, and accused the Houthis of “recent targeting of civilians”. The Red Sea is home to one of the world’s most vital trade routes through the Strait of Hormuz.

US President Joe Biden’s administration formally delisted the Houthis as a “foreign terrorist organization” and “specially designated global terrorists” in 2021, undoing a move by former President Donald Trump. The United Nations and aid groups had criticised the designations, saying their restrictions complicated aid deliveries to war-torn Yemen.

The Houthis – an Iran-backed group that controls large swathes of northern Yemen and the capital, Sanaa – have carried out attacks on Israel in recent weeks, launching missiles and drone attacks and threatening to seize Israeli vessels in the Red Sea.

Houthi forces raided a ship named Galaxy Leader on Sunday.  Houthi General Ali Al-Moshki said in later remarks on television: “Israeli ships are legitimate targets for us anywhere.”

The ship is operated by a Japanese firm and has links to Israeli businessman Abraham “Rami” Ungar.

The crew of that ship, composed of 25 workers from numerous countries, continue to be held by the Houthis. Kirby called for their immediate and unconditional release and accused Iran of being complicit in such attacks.

The raid, which analysts have said mirror tactics used by Iran, has raised alarm that the Houthis could step up such attacks in the Red Sea.

The group considers itself a member of the “axis of resistance”, a network of armed groups throughout the region backed by Iran and hostile to Israel and the US.

That Biden administration’s reversal of the “terror” designations for the Houthis was made to facilitate the delivery of humanitarian aid to Yemen, where the group has been locked in conflict with the government and a Saudi-backed coalition since 2015.

The Biden administration has considered redesignating the Houthis as a “terrorist” group at least one other time since then after drone and missile attacks on the United Arab Emirates claimed by the group.