“The firing of top officials like Sally Yates and Preet Bharara, and now Mr. Comey does not seem to be a coincidence.”

US Democrats have reacted angrily to President Donald Trump’s decision to sack FBI Director James Comey, saying it raises serious questions as the agency is investigating his election campaign’s alleged links to Russia’s meddling in the US polls.

“I told the president, ‘Mr President, with all due respect you are making a big mistake,’” the top Democrat in the Senate, Chuck Schumer, told reporters.

The Senate Minority Leader demanded that the Department of Justice appoint a special prosecutor to look into allegations of Russian hacking and its influence on the 2016 elections.

“The American people need to have faith that an investigation as serious as this one is being conducted impartially, without a shred of bias. The only way the American people can have faith in this investigation is for it to be led by a fearless, independent special prosecutor,” he said.

The firing of top officials like Sally Yates and Preet Bharara, and now Mr. Comey does not seem to be a coincidence, Schumer said. “This investigation must be run as far away as possible from this White House and as far away as possible from anyone that President Trump has appointed.”

Schumer also questioned the timing of the shock decision, which came days after Mr. Comey testified on Capitol Hill about the FBI’s investigation into Russia’s election meddling and a possible collusion between the country and Mr. Trump’s campaign.

“If the administration had objections to the way Director Comey handled the Clinton investigation, they had those objections the minute the president got into office. But they didn’t fire him then. Why did it happen today?” he asked.

“Were these investigations getting too close to home for the president? It is troubling that Attorney General Sessions, who had recused himself from the Russian investigation, played a role in firing the man leading it,” he said.

House Democratic Caucus Chairman Joe Crowley said Mr. Comey’s dismissal is extremely troubling.

“President Trump fired the man investigating him and his cohorts. I strongly support calls for the appointment of a special prosecutor,” he said.

Terming the move as “nearly unprecedented”, Indian-American Congressman Raja Krishnamoorthi said it was extremely disturbing that the Chief Executive is interfering with an ongoing investigation into his administration by firing the person charged with conducting it.

“One cannot help but be reminded of President Nixon’s Saturday Night Massacre. This action only raises further questions regarding the administration’s ties to Russia,” Mr. Krishnamoorthi said.

Republican Senator John McCain, Chairman of Armed Services Committee said he is disappointed by Mr. Trump’s decision to dismiss Mr. Comey.

“James Comey is a man of honor and integrity, and he has led the FBI well in extraordinary circumstances. I have long called for a special congressional committee to investigate Russia’s interference in the 2016 election,” he said.

“The president’s decision to remove the FBI Director only confirms the need and the urgency of such a committee,” Mr. McCain said.