A U.S. treasury official warned of environmental risks from illicit transfers of Iranian oil off Malaysia, news portal Malaysiakini reported on Thursday, as the United States narrows its focus on financing for militant groups routed through Southeast Asia.

The United States sees Iran’s capacity to move its oil as being reliant on service providers based in Malaysia, a senior U.S. treasury official said this week.

The official also said the United States was attempting to prevent Malaysia from becoming a jurisdiction where the Palestinian militant group Hamas could raise and transfer funds.