New Delhi, Sept. 5 -- The United States has sanctioned a Turkish investment bank and two of its subsidiaries over alleged financial links to Iran, marking a significant expansion of Washington's campaign to cut Tehran off from international finance.

The US Treasury Department on Friday designated Istanbul-based Golden Global Yatirim Bankasi Anonim Sirketi, along with Golden Global Portfoy Yonetimi Anonim Sirketi and Golden Global Varlik Kiralama Anonim Sirketi. All three were added to the Treasury's Specially Designated Nationals list, effectively cutting them off from the US financial system and dollar-based transactions.

Washington says the bank provided important financial access for Iran's shadow banking network and facilitated tens...