The Biden administration levied sanctions on Thursday on prominent Turkish businessman Sitki Ayan and his network of firms, accusing him of acting as a facilitator for oil sales and money laundering on behalf of Iran’s Revolutionary Guard Corps (IRGC). Ayan’s companies have set up international sales contracts for Iranian oil, arranged shipments, helped launder the proceeds and obscured the origin of the Iranian oil on behalf of Iran's Quds Force, an arm of the IRGC, the Treasury Department said in a statement reported by Reuters. “Ayan has established business contracts to sell Iranian oil worth hundreds of millions of dollars to buyers,” in China and Europe, it said, adding that he then funneled the proceeds back to the Quds Force. Ayan’s son Bahaddin Ayan, his associate Kasim Oztas and two other Turkish citizens involved in his business network are also designated, along with 26 companies, including his ASB Group, a Gibraltar-based holding company and a vessel. Bahaddin and Oztas were not immediately available for comment. Ayan’s ASB Group and Türkiye’s communications directorate did not immediately respond to requests for comment. The Treasury action freezes any US assets of those designated and generally bars Americans from dealing with them. People engaging in certain transactions with those designated also risk sanctions. The US measures come at a time of strained ties between the two nations over a host of issues, including disagreement over Syria policy and Ankara’s purchase of Russian air defense systems. Washington maintains sweeping sanctions on Iran. It has looked for ways to increase pressure as efforts to resurrect a 2015 nuclear deal with Tehran have stalled. President Joe Biden had sought to negotiate Iran's return to the nuclear deal after former President Donald Trump pulled out of it in 2018.