Washintgon, Mar 17 (IANS): US President Donald Trumps former national security adviser Michael Flynn was paid over $65,000 by companies linked to Russia in 2015, media reports said.

According to a letter released on Thursday by congressional investigators, Flynn received payments from the Kremlin-backed RT network, as well as from two separate Russian companies.

In the letter, FBI director James Comey and Defense Secretary Jim Mattis requested additional documents related to Flynn's security clearances, New York Times reported.

The letter and supporting documents provide new details about a trip Flynn took to Moscow in December 2015 on behalf of RT. As part of that trip, RT paid him more than $45,000 to deliver a speech at a gala hosted by the network, where he sat next to the Russian president, Vladimir Putin.

According to an invoice included with the letters, Flynn also received $11,250 from a Russian cargo airline named Volga-Dnepr Airlines.

In October 2015, Flynn was paid another $11,250 by Kaspersky Government Security Solutions. The Moscow-based firm has long been suspected of having ties to Russian intelligence services.

Flynn resigned as Trump's national security adviser in February, amid controversy over discussing US sanctions against Russia with Russian ambassador Sergey Kislyak in December.

The White House has claimed Trump was unaware of Flynn's work on behalf of a foreign government when he selected Flynn to serve as national security adviser.