Donald Trump asked James Comey, the former FBI director, to end an investigation into Michael Flynn's links to Russia, it was reported on Tuesday night.

“I hope you can let this go,” Mr Trump reportedly told Mr Comey, the day after Mr Flynn, the former national security adviser, had resigned over his undeclared contacts with Moscow.

The New York Times cited a memo that Mr Comey wrote shortly after the meeting with the US president in early February. Mr Trump fired Mr Comey, who was leading the investigation into links between the Trump campaign and Russia, last week.

If confirmed, it would be evidence that the US president had directly tried to influence the FBI investigation.

Calls for impeachment

Democrats said such an act would classify as an obstruction of justice and that Mr Trump could face impeachment.

"We are witnessing an obstruction of justice case unfolding in real time," Connecticut Sen. Richard Blumenthal, a Judiciary Committee member and former federal prosecutor, said in a statement. He called for the appointment of a special prosecutor to investigate.