It came as a current White House official was identified as a "significant person of interest" in the investigation into any coordination between the Trump campaign and Russian Federation, the Washington Post reported. The individual was described by people familiar with the matter as being "someone close to the president", although the sources declined to name names. This is in addition to former Trump aides Michael Flynn and Paul Manafort, who were previously identified as subjects of the investigation.
It did not deny the Times report that Trump was critical of Comey to the Russians the day after he fired him.
Rosenstein, who met behind closed doors with House members on Friday and senators on Thursday, has named Robert Mueller, a former FBI director, as special counsel under his authority to oversee the investigation of Russian meddling in last year's election and whether anyone close to Trump colluded in it. Attorney General Jeff Sessions has recused himself from the probe. "He was insane, a real nut job", Trump said, according to a report based on a summary of the meeting obtained by the Times.
"It explicitly usurped the role of the attorney general, the deputy attorney general and the entire Department of Justice, " Rosenstein said of that public announcement.
The FBI's investigation is focused on whether and to what extent Trump campaign and transition team officials were in contact with Russian officials to interfere in the 2016 election. But he said he had no intention of it being used that way.
In Rosenstein's meetings with lawmakers, he reiterated the scathing critique laid out in his memo concerning Comey's handling of the investigation into Hillary Clinton's use of a private email server, including Comey's July news conference announcing that the FBI would not recommend charges.
In response to the story the White House said that Mr Comey's "grandstanding" and "politicising" of the Russian inquiry hurt diplomatic efforts with Moscow.
The Justice Department issued the text of Mr Rosenstein's opening remarks for the briefings on Capitol Hill.
In meetings behind closed doors with politicians on Thursday and Friday, Mr Rosenstein said he wrote the memo after Mr Trump told him one day before the 9 May sacking that he wanted to dismiss Mr Comey.
Trump has said he expected to nominate a new Federal Bureau of Investigation director soon, and that had been expected before his departure Friday afternoon. Trump has insisted at times that the decision was his alone, but he also has pointed to the "very strong" recommendation from Rosenstein. "I believe it. I stand by it".
Trump has reacted furiously to the appointment of a special counsel, a prosecutor with wide authority to investigate Russia's interference and other potential crimes uncovered.