The Haberturk newspaper on Saturday reported that six banks potentially face substantial fines, citing senior banking sources. It did not name the banks. One bank faces a penalty in excess of $5 billion, while the rest of the fines will be lower, it said.

The report comes as relations between Washington and Ankara have been strained by a series of diplomatic rows, prompting both countries to cut back issuing visas to each other’s citizens.

U.S. authorities have hit global banks with billions of dollars in fines over violations of sanctions with Iran and other countries in recent years.

U.S. prosecutors last month charged a former Turkish economy minister and the ex-head of a state-owned bank with conspiring to violate Iran sanctions by illegally moving hundreds of millions of dollars through the U.S. financial system on Tehran’s behalf.