The US has blacklisted a businessman with ties to Turkey’s president and a network of his companies for allegedly arranging oil sales and shipments for Iran’s Qods Force.

Sitki Ayan, who is described in press reports as a confidant of Turkish President Recep Tayyip Erdogan, is accused of running a sanctions evasion network that has facilitated the sale of millions of dollars of oil for the Islamic Revolutionary Guard Corps (IRGC) Qods Force.

The US Treasury Department action targets Ayan, his ASB Group of Companies, several affiliated outfits and executives, an IRGC associate, and an LPG carrier and its registered owner.

The move follows a sanctions efforts in May aimed at tackling the revenue streams of Qods Force, a military intelligence arm of the IRGC.

“The US will continue to strictly enforce sanctions on the IRGC’s illicit oil sales trade,” said Brian Nelson, under secretary of the Treasury for terrorism & financial intelligence.

TradeWinds was unable to reach Ayan through ASB, where he is chairman and director, after business hours in Istanbul on Thursday.

The Treasury alleged that Ayan used his business network to facilitate and conceal sales and shipments of Iranian oil in partnership with Qods Force officials.

Officials said he used Baslam Nakliyat Ye Dis Ticaret, a company associated with ASB Group, to carry out the oil deals in a way that obscured their Iranian connection, and the firm’s bank accounts were allegedly used to move Qods Force money.

Another outfit, Baslam Petrol Sanayi Ve Ticaret Anonim Sirketi, is accused of facilitating the trade of Iranian oil to Chinese purchasers.

And another company, Anka Enerji Uretim Sanayi Ve Ticaret Anonim Sirketi, is accused of purchasing Iranian oil using $6m in falsified bills of lading.

The US also blacklisted the 37,500-cbm LPG carrier Queen Luca (built 1995) and its registered owner, Elvegard Shipping, on accusations that ASB Group officials set up the Marshall Islands company as a front to buy the vessel on behalf of Qods Force.

And Ayan’s son, Bahaddin Ayan, has been placed on the Treasury Department blacklist alongside Bumerz Denizcilik Ve Ticaret Anonim Sirketi, where he is on the board of directors. The company, also known as Bumerz Shipping, was once used to purchase a tanker on behalf of Sitki Ayan, US officials said.

The Politico website reported on Thursday that Ayan is a long-time friend of Erdogan who went to the same high school as the Turkish president.

The sanctions strike at a man close to Erdogan came shortly after the Treasury Department urged Turkey to drop its requirement to require additional protection and indemnity insurance for tankers transiting the Bosphorus.

TradeWinds reported earlier on Thursday that P&I clubs have refused to comply with the requirement introduced on 1 December, a few days before the West tried to impose a price cap on Russian oil. Turkey responded by refusing to allow at least 21 laden tankers to use the waterway.