Sessions' testimony came in the wake of fired FBI Director Comey's assertion that he believed he was sacked by Trump as part of an effort to influence the agencies' investigation into Russia's meddling in the presidential polls.
Trump later said he had planned to fire Comey regardless of what recommendation he received from Rosenstein and Attorney General Jeff Sessions, who has recused himself from the Russian Federation investigation.
On Wednesday the Post reported that five unnamed sources said Mueller is investigating whether Trump obstructed justice by seeking to end a probe of a former top national security adviser and firing FBI Director James Comey, and The New York Times used unnamed sources to report that Mueller had requested interviews with three top intelligence officials.
In addition, reports surfaced that US Vice President Mike Pence has hired a personal lawyer to deal with requests from the special counsel investigating possible collusion with Russian Federation during the 2016 election, a top aide said Thursday.
The bipartisan Senate Intelligence Committee's deep dive into Russia's election meddling, which President Donald Trump has suggested is a hoax perpetrated by the media and sore-loser Democrats, will continue next week with a hearing on the cybersecurity outlook for the next election.
The special counsel appointed to probe alleged Russian meddling in the 2016 United States presidential polls is now also investigating President Donald Trump for possible obstruction of justice, according to a media report. "Witch Hunt", the president wrote in his tweet.
In a second Tweet, Trump echoed previous claims that he is the victim of what he says is the "single greatest witch hunt in American political history".
"They made up a phony collusion with the Russians story, found zero proof, so now they go for obstruction of justice on the phony story". But soon after the abrupt termination, Trump told NBC News that he had been going to fire Comey regardless of any recommendations. "Witch Hunt", Trump wrote on Twitter.
Friday's tweets are the latest in a week of angry social media responses by the president over a report by The Washington Post that Mueller was looking into whether Trump obstructed justice. A day later, Rosenstein appointed Mueller, who was at the helm of the Federal Bureau of Investigation during the September 11 attacks, as special counsel.
Investigators have also been looking for any evidence of possible financial crimes by Trump associates, the daily said, quoting unnamed U.S. officials. "It would be standard practice for the Special Counsel to examine financial records to look for anything related to Russia", Gorelick told the Washington Post.
Comey testified last week that he also felt pressured to drop the Flynn probe.
The transition order came the same day that Vice President Mike Pence's confirmed that he had hired a private lawyer to represent his interests in the expanding probe.
The first is into whether anyone on Mr Trump's campaign or associated with it, with him or with any of his businesses, may have had any illegal dealings with Russian officials or others with ties to the Kremlin, said the official.
Mr Pence's office confirmed he had retained Richard Cullen, a former Virginia attorney general and United States attorney for the Eastern District of Virginia, to assist "in responding to inquiries" from Mr Mueller.