A US Senate panel investigating possible Russian interference in US elections and possible collusion with President Donald Trump's campaign team has requested that James Comey, the sacked FBI director, testify before its members.

The Senate Intelligence Committee's Republican chairman and Democratic vice chairman sent a letter to Comey "seeking his appearance before the [committee] in both open and closed sessions", the panel said in a statement on Wednesday.

The statement also said the panel had asked Andrew McCabe, acting FBI director, to send any notes or other memos prepared by Comey about communications he may have had with senior White House and Department of Justice officials in relation to the investigation into Russia and the 2016 election.

Democratic Senator Mark Warner told US media he believed "the American people will get a chance to hear from Comey shortly".

Warner would not say if Comey accepted the invitation.

On Tuesday, the House Intelligence Committee also requested similar documents from the FBI.

The decision came hours after a report by the New York Times that claimed Trump asked Comey to end the agency's investigation into ties between Michael Flynn, former White House national security adviser, and Russia.

It had already been a week of tumult at the White House after Trump dismissed Comey and then discussed sensitive national security information about the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group with Sergey Lavrov, Russia's foreign minister.

In another development on Wednesday, Democratic Representative Al Green called for Trump's impeachment.

"This is about what I believe. And this is where I stand. I will not be moved. The president must be impeached," said Green who is the first member of Congress to officially request levelling charges against the president.

With news of the Comey memo, Democrats have increased their talks about impeaching Trump.

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