Adam Schiff, the highest-ranked Democrat on the House Intelligence Committee, said this intervention by Mr Trump, if confirmed, amounted to "interference or obstruction of the investigation".
Comey wrote that Trump asked him to drop a probe of former national security adviser Michael Flynn, a day after the president dismissed Flynn. At their news conference, Ryan and other House Republican leaders talked about National Police Week and their plans to overhaul the United States tax code before reporters raised questions about the Trump controversies.
The White House has said that Flynn was dismissed for misleading Vice President Mike Pence about a phone call with the Russian ambassador, during which he reportedly discussed ways of softening USA sanctions on Russia.
The White House has played down the importance and secrecy of the information Trump gave to the Russians, which came from Israel under an intelligence-sharing agreement. Trump himself said he had "an absolute right" as president to share "facts pertaining to terrorism" and airline safety with Russian Federation. Reports that this information was provided by a USA ally and shared without its knowledge sends a troubling signal to America's allies and partners around the world and may impair their willingness to share intelligence with us in the future.
Republican Sen. Charles Grassley of Iowa and Democratic Sen.
Chairman Richard Burr, a North Carolina Republican, and Vice Chairman Mark Warner, a Democrat from Virginia, said they have asked Comey to testify before the panel in both open and closed sessions.
The president ignored shouted questions from reporters Wednesday as he left the White House to address a graduation ceremony at the U.S. Coast Guard Academy in CT, where a complaint about media coverage was his only reference to the controversy swirling around him. "You can't let them get you down", he said.
Top members of the Senate Judiciary Committee have asked the Federal Bureau of Investigation to provide memos from Comey and for the White House to turn over any audio recordings that might exist of conversations with the now-fired director.
White House Denial No one from the administration would respond to the memo on the record.
The person who described the Comey memo to the AP was not authorized to discuss it by name and spoke on condition of anonymity.
Obama, shortly after last November's presidential election, reportedly warned Trump not to hire Flynn for the national security post, according to news reports - advice the billionaire businessman failed to heed. Instead, the White House press office released an emailed statement denying Comey's version of events.
The Russia story has already claimed one victim - Mr Trump's first national security adviser Michael Flynn, who was sacked after misleading the government over his meetings with Mr Kislyak.