A top congressman probing Russia's role in the presidential race pledged Thursday to find out how much the FBI relied on a dossier on then-candidate Donald Trump that is so sensational it would make the "National Enquirer blush," Fox News reported.

Rep. Trey Gowdy, chairman of the House Oversight Committee, told Fox that new revelations into a related investigation of the sale of 20 percent of the U.S. uranium stockpile to a Russian company have increased the focus on the multiple probes into Moscow's efforts to influence last year's election.

Gowdy, a South Carolina Republican and former prosecutor, said he is particularly concerned about how much the FBI relied on a report compiled by a shadowy Washington, DC, opposition research firm.

The report, based on the work of a former British spy and his contacts in Russia, claim Trump cavorted with prostitutes in a Moscow hotel room and had suspicious contacts with Russian oligarchs tied to President Vladimir Putin. The Washington Post reported this week that the Democratic Party and Hillary Clinton's presidential campaign paid for the report.

"What is most important to me, is whether or not the world's premier law enforcement agency relied upon a piece of investigative work that would make the National Enquirer blush. That is what I want to know. Whether or not the FBI relied upon it to launch an investigation and whether or not they relied upon it in court filings," Gowdy told Fox News.

He also noted that congressional investigators want to interview an FBI source who reportedly has first-hand knowledge of a bribery and kickback scheme related to Russia's acquisition of 20 percent of the U.S. uranium stockpile.

The State Department approved that sale when Hillary Clinton was secretary of state and her husband, former President Bill Clinton, was paid $500,000 for a speech in Moscow, according to The Daily Mail.

The Justice Department Wednesday removed a gag order imposed under the Obama administration that prevented the informant from publicly discussing what he knew about the transaction, The Hill reported.

Asked what he wants to hear from the FBI informant, Gowdy responded, "Whatever he has."