The entities targeted are Instanbul-based investment bank Golden Global Yatirim Bankasi Anonim Sirketi, asset manager Golden Global Portfoy Yonetimi Anonim Sirketi and asset leasing company Golden Global Varlik Kiralama Anonim Sirketi, according to the Treasury's Office of Foreign Assets Control.
The sanctions put all three entities on the Treasury's OFAC Specially Designated Nationals list, cutting them off from the US-dollar-based financial system.
The Treasury also issued a general licence to allow the wind-down of transactions with the sanctioned entities.
In an interview with news outlet America's Voice News, US Treasury Secretary Scott Bessent said the latest action "is code for you are out of business".
"And we will probably sanction another bank next week, and we are telling the financial system bad actors: 'We know who you are, you know who you are, it's over, and our allies are helping with this," he said.
Golden Global Yatrim Bankasi is the 35th-largest bank in Turkey by total assets, according to database TheBanks.EU, with total assets of 25,024.68 million Turkish lira ($A716.86 million) in 2025.
The bank did not immediately respond to a request for comment.
The Treasury said in a statement that Golden Global was established for the purpose of enabling Iran's shadow banking network to transfer oil revenues from China to Turkey, where it could then be converted to cash and gold by money exchangers.
It said Golden Global has knowingly offered to provide correspondent banking services to Iranian financial institutions, enabling transactions through accounts controlled by the Islamic Revolutionary Guard Corps Qods Force and its proxies.
The action is the latest in the administration of US President Donald Trump's campaign to economically pressure Iran six months into the US-Israel war with Iran, which has pushed energy prices higher worldwide.
Bessent, who in August announced an "economic onslaught" against Iran's financial links around the world, has said the US is seeking to force Iran back to the negotiating table.
Last week, the United States moved to impose Patriot Act curbs on Egyptian lender Banque Misr's branches in the United Arab Emirates from US dollar transactions over their dealings with Iran.
But the action fell short of full OFAC sanctions on the institution that did not affect Misr's head office or branches elsewhere.
In an interview with Reuters on Sunday, Bessent said the Treasury Department was likely to roll out new secondary sanctions every week, initially focusing on banks, as part of a broader campaign to intensify economic pressure on Iran.
Sanctions expert Brett Erickson, managing principal of Obsidian Risk Advisors, questioned how effective the action would be and said it could draw retaliation from Iran.
"The sanctioning of Golden Global will marginally increase pressure on Iran. But hurting Iran and changing the outcome of this war are two very different things," Erickson said.
"If this pressure cannot meaningfully change the economic trajectory of the war, Washington may simply be poking the bear and daring Iran to retaliate in ways that could inflict far greater damage on the global economy," Erickson said.
