By Jim Sciutto and Tom LoBianco

CNN

(CNN) -- A pair of top House Democrats are digging into whether former national security adviser Michael Flynn may have misled officials on his security clearance form about two Middle East trips -- including one reportedly about building $100 billion worth of nuclear energy plants with help from Russia's nuclear power agency.

The top Democrats on the House oversight committee and the House foreign affairs committee sent a request to Flynn's lawyers -- as well as two consultants -- seeking additional documents about a summer 2015 trip he took to the Middle East to float a nuclear energy deal involving Russia.

The letter cites a recent Newsweek article detailing Flynn's previously undisclosed trip and a plan that involved Saudi Arabia selling energy from the nuclear projects to US allies in the Middle East and a promise from those Gulf countries to purchase $100 billion in arms from Russia that otherwise would have been sold to Iran.

Rep. Elijah Cummings, the top Democrat on the oversight committee, and Rep. Eliot Engel, the top Democrat on the foreign affairs committee, also asked for more details about an October 2015 trip Flynn took to the Middle East, citing details from Flynn's security clearance, including what Flynn told investigators. The hotel Flynn says he stayed at does not exist, and there is no record of a travel companion he took with him, Cummings and Engel wrote.

The request comes just two months after the House oversight committee revealed that Flynn never documented payments he received from RT-TV, generally considered to be an arm of the Russian government, on his 2016 application for a renewed security clearance. Then-House oversight Chairman Jason Chaffetz noted at the time that Flynn may have broken the law, but also said that was not a determination for congressional investigators to make.

House investigators note that they do not know precisely when Flynn traveled to the Middle East for the nuclear deal, but they cite a discrepancy between the June 10, 2015 testimony he gave to the House Foreign Affairs Committee and his official August 2015 start date he lists with Hewlitt's consulting company.

Investigators note Flynn testified on June 10 that he had taken a recent trip to the Middle East and discussed nuclear power issues, and one week after he testified, Saudi Arabia and Rosatom (Russia's nuclear energy agency) signed a deal.

At the time of his House testimony, Flynn said he was testifying on behalf of his Flynn Intel Group and had not received any money from a foreign government related to the subject of the hearing.

Cummings and Engel said Monday that the broader pattern has led them to pry deeper into the information Flynn has left off of his 2016 security clearance application.

"Most troubling of all, we have no record of Gen. Flynn identifying on his security clearance renewal application -- or during his interview with security clearance -- even a single foreign government official he had contact with in the seven years prior to submitting his security clearance application," Cummings and Engel write in their June 19 letter.

The investigators also sent the request for information to Rear Adm. Michael Hewitt and Alex Copson, a pair of energy and security consultants who reportedly worked with him on the Saudi-Russia nuclear proposal.

A lawyer for Flynn, Rob Kelner, declined comment in an email Monday. CNN was unable to immediately reach Hewitt or Copson Monday afternoon, despite trying multiple listed phone numbers.

House Republicans had not signed onto the request as of Monday afternoon. Spokespeople for House oversight Chairman Trey Gowdy and House foreign affairs Chairman Ed Royce were not immediately available for comment Monday afternoon.