The US Department of the Treasury announced Thursday that it and the Turkish government have identified and frozen the assets of a “key [ISIS] financial facilitation network” based in Mersin, Turkey. The asset freeze targeted four individuals and two entities in Turkey that were accused of assisting ISIS with transferring funds between Iraq and Syria. The US designated the individuals and companies under Executive Order 13224, and Turkey froze their assets.

Executive Order 13224 was initially signed by President George W. Bush in 2001 and allows the US to “disrupt the financial support network” of terrorist organizations by blocking the assets of both terrorist organizations and any who assist them. It has been renewed by every administration since. Under Secretary Brian Nelson heralded the joint action as being “a result of close coordination and collaboration with our Turkish partners”.

The US recently used the order to block the assets of four South African ISIS cell members in November. In June, the Treasury Department used the order to sanction two Russians connected to the far-right Russian Imperial Movement.

E.O. 13224 previously faced a legal challenge in 2009, with the Humanitarian Law Project claiming that the order’s provision against providing services to terrorist organizations was unconstitutionally vague. While that challenge was dismissed by a US appeals court, federal courts have previously held that the order’s use can be unconstitutional if there is an insufficient basis for designating an individual or entity.