WASHINGTON (Reuters) - U.S. Democratic lawmakers called on Wednesday for a congressional committee to issue subpoenas to the White House and three companies for documents about fired national security adviser Michael Flynn.

FILE PHOTO: Then White House National Security Advisor Michael Flynn walks down the White House colonnade on the way to Japanese Prime Minister Shinzo Abe and U.S. President Donald Trump's joint news conference at the White House in Washington, U.S., February 10, 2017. REUTERS/Jim Bourg/Files Photo

In a letter to Trey Gowdy, the Republican chairman of the House Government Reform Committee, the panel’s Democratic members said the committee should demand documents the White House has refused to hand over despite a bipartisan request in March.

Some of the documents are related to work on a proposal to build nuclear reactors in the Middle East with the involvement of Russian firms.

Three companies - Flynn’s consultancy and two companies he advised on the nuclear project -- have not produced documents and communications the committee’s minority members requested on September 15, and should be compelled to cooperate, the Democratic members said.

Flynn, a former national security adviser under President Donald Trump, is a central figure in a federal probe led by Special Counsel Robert Mueller into whether Trump aides colluded with Russia to boost his presidential campaign. Russia has denied interfering in the U.S. election and Trump has said there was no collusion.

In response to the Democrats’ request on Wednesday, Gowdy referred the matter to Mueller and Deputy Attorney General Rod Rosenstein, saying those kinds of allegations against Flynn should be handled by the justice department.

“Much of what is sought by my Democratic colleagues - if properly investigated, charged and proven beyond a reasonable doubt - would carry criminal penalties. Congress does not, and

cannot, prosecute crimes,” Gowdy said in the letter.

Flynn’s lawyer, Robert Kelner, declined to comment.

The committee has been probing whether Flynn fully disclosed payments from foreign sources and overseas trips when he renewed his Top Secret security clearance last year.

One focus of the probe is a June 2015 trip Flynn, a former general, took to Israel and Egypt to gauge interest in a plan floated by a group of scientists, consultants, and former military officers to build and provide security for dozens of nuclear power plants in the Middle East.

A promotional slide indicates that Rosoboron, a Russian state-owned arms exporter that is under U.S. sanctions, was to be part of the multi-billion dollar project.

SUBPOENAS

Trump fired Flynn in February after a top Justice Department official warned that the former Defense Intelligence Agency director could be blackmailed because Moscow knew he made misleading statements about his contacts with Russian officials.

In the letter, Democratic lawmakers argued that subpoenas were needed to determine whether Flynn was promoting the project while he was in the White House.

“We believe the paper trail must be pursued to answer the gravest question of all - did General Flynn seek to change the course of our country’s national security to benefit the same private interests he previously promoted,” the letter said.

The Democrats also pointed to a discrepancy between Flynn’s financial disclosures and statements to the committee by the counsel for IronBridge Group, Inc. and IP3 Corp., two companies set up by former Navy Rear Admiral Michael Hewitt and which are promoting one of two competing plans by U.S.-based consortiums for building nuclear reactors in the Middle East.

In an amended disclosure in August, Flynn said he served as an advisor to IronBridge from June 2016 to December 2016, a period that overlapped with his work on Trump’s presidential campaign and the post-election transition.

In contrast, the counsel for IP3 and IronBridge told the committee that the company tried to hire Flynn, but he never accepted the offer. The counsel said IP3 and IronBridge had split with members of another company -- ACU Strategic Partners -- and does not involve Russian entities in its nuclear plan.

A spokesperson for IP3 declined to comment.

ACU, which is promoting a plan that envisions the participation of government and private sector entities from Russia, Ukraine and Israel, among other countries, did not respond to a request for comment.