A top Democratic senator has asked Treasury Secretary Steven Mnuchin to share information about his relations with Turkish officials as part of an inquiry into whether he or other members of President Donald Trump's administration interfered with a U.S. criminal investigation into a Turkish state-owned bank.

Senator Ron Wyden of Oregon, the ranking Democrat on the finance committee, sent Mnuchin a letter on Wednesday raising concerns over "troubling reports" about the Treasury secretary's alleged involvement with the treatment of Halkbank, one of Turkey's largest banks.

Wyden referred to a Bloomberg News report published earlier this month that Trump assigned Mnuchin and Attorney General William Barr to deal with Turkish President Recep Tayyip Erdogan's repeated pleas to avoid charges against Halkbank.In an April phone call, Trump told Erdogan that Mnuchin and Barr would handle the issue, according to people familiar with the matter. In the months that followed, no action was taken against Halkbank for its alleged involvement in a plan to evade sanctions on Iran. That changed when an undated indictment was unveiled last week -- a day after Trump imposed sanctions over Turkey's military operation in northern Syria.

"The administration's interference in favor of Turkey's Halkbank requests could have undermined years of effort by U.S. law enforcement," which dates back to 2012, Wyden wrote in a letter obtained by Bloomberg News.In 2017, Trump pressed then-Secretary of State Rex Tillerson to help persuade the Justice Department to drop a criminal case against Reza Zarrab, an Iranian-Turkish gold trader who was a client of Trump's personal lawyer, Rudy Giuliani, according to people familiar with the matter. Tillerson refused, saying it would be illegal.

"These reports are part of a larger story highlighting Trump's efforts to accommodate the intense pressure campaign by the Turkish government to get investigations into Halkbank dropped," Wyden said in the letter to Mnuchin.

He requested that Mnuchin share details of all interactions with Turkish officials since taking office. Wyden asked if Trump or anyone at the president's direction asked Mnuchin to intervene with Turkish concerns regarding Halkbank, and whether the Treasury secretary ever appealed to the Justice Department on behalf of the bank.

Wyden set a Nov. 20 deadline for Mnuchin to respond.

Earlier this month, U.S. prosecutors filed criminal charges against Halkbank, accusing it of fraud, money laundering and violating U.S. sanctions against Iran. It's unclear exactly when the Halkbank indictment was filed, raising questions about whether it was set aside until it became politically expedient for the Trump administration to unseal it.

The charges against Halkbank also come after years of public and private lobbying by Erdogan and other top Turkish officials -- starting in the Obama administration -- to get the investigations into violations of Iran sanctions dropped.Wyden also sent separate letters to the chief executives of eight banks including JPMorgan Chase & Co., HSBC Holding Plc and Deutsche Bank AG that were identified in the indictment as "victim banks" tricked into processing barred transactions on behalf of Halkbank.

Wyden asked each bank to describe its relationship with Halkbank, due diligence policies and details about dollar transactions for foreign banks.