Senator and former Democratic presidential candidate Bernie Sanders says that Donald Trump’s sudden firing of former FBI Director James Comey has raised serious questions about what the President is trying to keep secret.

“Donald Trump’s decision to fire FBI Director James Comey raises serious questions about what his administration is hiding," Mr Sanders said in a statement.

"Why did President Trump fire the person leading the investigation into possible collusion between his campaign and the Russian government?”

Mr Sanders said that he was troubled by the timing of the firing of Mr Comey, which came a day after former acting Attorney General Sally Yates testified that she had warned the White House about former National Security Adviser Michael Flynn’s ties to Russia. Mr Comey was scheduled to appear before the Senate Intelligence Committee several days later.

“President Trump has repeatedly taken steps to kill inquiries into Russia’s involvement in the US election,” Vermont Senator Mr Sanders said.

“It is clear that whomever President Trump handpicks to lead the FBI will not be able to objectively carry out this investigation. We need an independent investigation into the Trump campaign’s ties to Russia.”

Mr Comey was fired unexpectedly by Mr Trump on the advice from the Justice Department. A memo written encouraging the former FBI official’s removal argued that Mr Comey had violated the public’s trust last year when he publicly announced that his bureau wasn’t recommending pressing charges against former Democratic presidential nominee Hillary Clinton for the use of a private email server as secretary of State.

Comey expects Russia to return to hack in 2018 and 2020

Mr Comey said then that the FBI had not found information indicating Ms Clinton or her team had acted in any way that would qualify criminal charges.