The U.S.’s top lawyer faced increasing scrutiny Wednesday after reports alleged he twice contacted Russian officials during the run-up to last year's presidential elections.

Jeff Sessions repeatedly denied any contacts with Russia when has was asked about possible communications during his Senate confirmation hearings, leading the ranking Democrat on the House Oversight Committee to demand his resignation.

"It is inconceivable that even after Michael Flynn was fired for concealing his conversations with the Russians that Attorney General Sessions would keep his own conversations secret for several more weeks," said Elijah Cummings. "Attorney General Sessions should resign immediately."

Sessions, who was a senator at the time. spoke twice to Russia's U.S. ambassador Sergey Kislyak - once in July and again in September, according to the Washington Post.

The September meeting took place in Sessions' Capitol Hill office "at the height of what U.S. intelligence officials say was a Russian cyber campaign to upend the U.S. presidential race", according to the newspaper.

The conversation in July took place on the sidelines of the Republican National Convention.

The attorney general denied he "ever met" with Russian officials "to discuss issues of the campaign”.

"I have no idea what this allegation is about. It is false."," he said in a statement.

A spokeswoman for Sessions denied he misled lawmakers during his testimony and pointed to mo re than 25 conversations he had with foreign ambassadors last year as a member of the Armed Services committee.

The ambassadors included representatives of the UK, South Korea, Japan, Poland, India, China, Canada, Australia, Germany and Russia, Sarah Isgur Flores said .

"He was asked during the hearing about communications between Russia and the Trump campaign--not about meetings he took as a senator and a member of the Armed Services Committee," she said.

Apparently unconvinced, House Minority Leader Nancy Pelosi said Sessions lied under oath and as a consequence he must now resign.

"Sessions is not fit to serve as the top law enforcement officer of our country and must resign," she said in a statement.

None of the senators serving on the Senate Armed Services Committee told the Washington Post they met with Russia's Washington envoy.

But only 20 of the 26 members responded to the newspaper's queries.