Michael Flynn (right) is a central figure in a federal probe into alleged collusion between the Trump presidential campaign and Russia. Pic/AFP
Michael Flynn (right) is a central figure in a federal probe into alleged collusion between the Trump presidential campaign and Russia. Pic/AFP

Democratic lawmakers are probing whether retired US General Michael Flynn secretly promoted a US-Russian project to build dozens of nuclear reactors in the Middle East after becoming President Donald Trump's first national security adviser.

Representatives Elijah Cummings and Eliot Engel made the disclosure in a letter they sent on Tuesday to Flynn's lawyer and executives of firms that developed the reactor scheme and for which Flynn's now-defunct consulting company worked. "The American people deserve to know whether General Flynn was secretly promoting the private interests of these businesses while he was a (Trump) campaign adviser, transition official, or President Trump's national security adviser," the two said in the letter made public on Wednesday.

They asked Flynn's lawyer and executives of companies involved in the project to provide "all communications" they had with Flynn or other administration officials during the 2016 campaign, the post-election transition or Flynn's tenure as national security adviser. Robert Kelner, Flynn's lawyer, declined to comment.