WASHINGTON (Reuters) – The U.S. imposed sanctions on Monday on three vessels and their owners for delivering oil and gas products to Yemen’s Houthis, as Washington piled pressure on the Iran-backed rebels over their attacks on Red Sea shipping.

The sanctions targeted Marshall Islands-registered Zaas Shipping & Trading Co and Great Success Shipping Co, and Mauritius-registered Bagsak Shipping Co and the cargo vessels they used to deliver oil and gas products to the Houthi-controlled port of Ras Isa, the U.S. Treasury Department said in a statement.

“Today’s action underscores our commitment to disrupt the Houthis’ efforts to fund their dangerous and destabilizing attacks in the region,” Deputy Secretary of the Treasury Michael Faulkender said.

The sanctions came hours after Houthi-controlled television said a U.S. airstrike killed 68 people at a detention center for African migrants in Yemen.

In March, the U.S. designated the Houthis as a “Foreign Terrorist Organization,” accusing the group of threatening the security of American civilians and personnel in the Middle East as well as partners in the region and global maritime trade.

The attacks on ships, which the Houthis say are in solidarity with Palestinians in Gaza, have disrupted global commerce, stoked fears of inflation and deepened concern about the fallout from the Israel-Hamas war.

The group has controlled the most populous parts of Yemen, including the capital Sanaa, since it ousted the government in 2014.

“The United States is committed to disrupting the Houthis’ illicit revenue generation, financial facilitators, and suppliers as part of our whole-of-government approach to eliminating threats to freedom of navigation in the Red Sea,” State Department spokesperson Tammy Bruce said in a statement.

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(Reporting Katharine Jackson and Daphne Psaledakis; Editing by Doina Chiacu and David Gregorio)