US president Donald Trump's former national security adviser, Michael Flynn, was warned when he retired from the military in 2014 not to take foreign money without "advance approval" by Pentagon authorities, newly released documents show.
The US defence department inspector general's office confirmed in a separate document that it is investigating whether Mr Flynn failed to obtain prior approval.
The chairman and senior Democrat on the US House Oversight Committee want the US Army to rule on whether Mr Flynn informed it about and asked permission for payments from Russian and Turkish entities.
Mr Flynn earned tens of thousands of dollars from Russia's state-sponsored RT television network and from a Turkish businessman linked to the government in Ankara.
A strong voice during Mr Trump's election campaign, Mr Flynn was sacked as the president's national security adviser in February.