The US Department of the Treasury’s Office of Foreign Asset Control (OFAC) added 12 individuals, entities and vessels to the Specially Designated Nationals (SDN) list Thursday for funding Houthi efforts in Yemen.

In a press release, the Treasury said that the newly designated persons were engaged in a smuggling operation. The effort was led by Iranian-based Sa’id al-Jamal, who used a complex network of intermediaries to sell Iranian oil. The sale of this oil generated tens of millions of dollars, which was used to fund Houthis in Yemen and the Quds Force in Iran.

The Yemeni Civil War has been called one of the world’s worst humanitarian crises. Houthis, allegedly supported by Iran, North Korea, Syria, and Russia, have fought against the Abdrabbuh Mansur Hadi-led Yemeni government since 2015. The government is backed by a Saudi Arabia-led coalition, the US, NATO, and Israel. UN experts have asked the UN Security Council to refer the alleged human rights abuses in this conflict to the International Criminal Court.

OFAC’s designation of these individuals, businesses, and vessels as Specially Designated Nationals will increase the hurdles they face in smuggling Iranian oil. Persons on the SDN list have their US assets blocked and US persons are prohibited from doing business with them. As a result, they will not be able to access or use the US financial system, as banks are prohibited from working with them.