Mr Mueller was appointed as special counsel to investigate Moscow's involvement in the presidential election a year ago and possible collusion by Trump campaign associates with the Russians, but there has been no indication that Mr Mueller told the president to fire Mr Comey. "Witch Hunt", Trump wrote on Twitter.
And he appeared to accuse Mr Rod Rosenstein, the Deputy Attorney-General, of leading a "witch hunt". Following Washington Post reports about the obstruction of justice investigation and White House senior advisor Jared Kushner being looked at over his business dealings, Rosenstein sent out a unusual statement last night claiming "anonymous allegations" should not be trusted.
In recent days, news has also surfaced of the legal team Mr. Mueller has assembled.
Dianne Feinstein, top Democrat on the Senate Judiciary Committee, said she was "increasingly concerned" that Trump will fire both Mueller and Rosenstein.
The Democratic National Committee (DNC) called on Rosenstein to recuse himself from the Russian Federation matter, but said authority over the investigation should be given to Mueller and not another Trump appointee. Grassley's office said the letter is in response to a recent letter from Feinstein requesting that the committee seek details from senior Federal Bureau of Investigation leadership about Comey's interactions with President Donald Trump before he was sacked. "That's undemocratic on its face and a blatant violation of the president's oath of office".
Rosenstein has been overseeing the Russian Federation probe since Attorney General Jeff Sessions recused himself. Comey's firing likely will be part of that probe.
Cladding used in London's Grenfell Tower is 'banned in Britain'
Two neighbouring Tube lines are to be partly suspended into a second day amid safety concerns of debris falling on to the tracks. Meanwhile, 19 people remained in hospital as of Saturday, of whom 10 were receiving critical care.
Earlier this month, Rosenstein told The Associated Press that "if anything that I did winds up being relevant to his investigation then, as Director Mueller and I discussed, if there's a need from me to recuse, I will". An official of Trump's transition confirmed the lawyer's internal order, which was sent Thursday. The aide spoke on condition of anonymity because the meeting was private.
The order by the general counsel for the transition team casts a wide net on documents that could shed light on ties between Trump's presidential campaign and representatives of Russia's government. The White House has denied any collusion.
The Twitter attacks came as Vice-President Mike Pence hired a personal lawyer to represent him in the intensifying investigation. Pence headed the Trump transition until Inauguration Day. The transition, a non-profit structurally separate from the Trump campaign, continues to operate with a small staff.
The president has denied that he has any nefarious ties to Russian Federation and has also disputed that he's attempted to block the investigation into his campaign's possible role in Russia's election-related hacking. The memo asks for preservation of electronic communications and data, telephone logs, audio recordings, videos, calendars and other items.
"I can go around them", Trump tweeted.
One lawyer who is involved in the case and knows Rosenstein well, said the veteran prosecutor is a mix of furious and amazed at Trump's tweets.