WASHINGTON (Reuters) - A top Democratic senator on Thursday questioned whether President Donald Trump interfered with a criminal investigation of Turkey’s Halkbank, which has been accused of conspiring to evade U.S. sanctions against Iran.

FILE PHOTO: People walk past by a branch of Halkbank in central Istanbul, Turkey, October 16, 2019. REUTERS/Huseyin Aldemir/

Oregon Senator Ron Wyden, the ranking member on the Senate Finance Committee, wrote to U.S. Treasury Secretary Steven Mnuchin asking if Trump or anyone acting on the president’s behalf had asked Mnuchin to “handle, intervene, or otherwise engage with Turkish concerns related to Halkbank, or with Halkbank generally?”

Wyden said he was launching an investigation to examine the relationship between Halkbank and Trump administration officials. The letter cited an Oct. 16 Bloomberg report that Trump told Turkish President Tayyip Erdogan in April that Mnuchin and U.S. Attorney General William Barr would handle the Halkbank issue.

Wyden said he expected an answer by Nov. 20.

U.S. federal prosecutors in Manhattan earlier this month charged Turkey’s second-largest state bank with fraud and money laundering, among other sanctions-related offenses, using sham food and gold transactions to get around U.S. sanctions.

Halkbank has denied the charges.

The U.S. court case has further strained tensions between Turkey and the United States, which have been at odds over a number of issues, including Ankara’s Syria incursion and purchase of a Russian missile defense system.

The charges against Halkbank are the latest development in a U.S. criminal case that became public in 2016 with the arrest in Miami of Reza Zarrab, a Turkish-Iranian gold trader accused of playing a central role in the sanctions evasion scheme.

Mehmet Hakan Atilla, a Halkbank deputy general manager, was arrested in New York the following year. He was sentenced to 32 months in prison following his conviction and was released and returned to Turkey earlier this year.

Zarrab pleaded guilty and testified for U.S. prosecutors at Atilla’s trial.

Before pleading guilty, Zarrab hired Rudy Giuliani, a longtime associate of Trump, to try to negotiate a deal between the U.S. and Turkish governments to secure his release.

Zarrab said that Iran, with the help of Halkbank and Turkish government officials, including Erdogan, used a complex web of shell companies and sham transactions in gold, food and medicine to get around U.S. sanctions.

Turkish officials raised Halkbank in their discussions with American counterparts last week, U.S. Vice President Mike Pence told a press conference in Ankara following the talks, which were focused on Syria.

Pence said the Turks were told this was a matter for the Southern District of New York, whose prosecutors brought the criminal case.

Turkey’s Erdogan has blasted the U.S. charges against Halkbank and called the case an ‘unlawful, ugly’ step.