A United States Senate panel investigating Russian interference in last year’s election has issued a rare formal demand for documents from President Donald Trump’s former national security adviser.

According to the Senate intelligence committee, Michael Flynn has failed to voluntarily co-operate with the investigation.

He was forced to resign in February after failing to disclose the content of his talks with Russian diplomats.

Meanwhile, the fallout has continued over the firing of the FBI director.

The White House maintained that James Comey was removed on Tuesday for his handling of the inquiry over Hillary Clinton’s emails.

But according to senior democrats he had recently asked the justice department for more resources for his Trump-Russia investigation.

Democrats have vowed that the house and senate intelligence committees’ investigations into the Russia claims would continue.