Top Democrats issued demands for Attorney General Jeff Sessions to immediately resign late Wednesday following news that he met with the Russian ambassador to the U.S. during the 2016 presidential campaign.

House Minority Leader Nancy Pelosi and Sen. Elizabeth Warren of Massachusetts were among those who called for the attorney general to step down.

Related: AG Sessions Had Contact With Russian Envoy During Campaign

"Sessions is not fit to serve as the top law enforcement officer of our country and must resign," Pelosi said in a statement. "There must be an independent, bipartisan, outside commission to investigate the Trump political, personal and financial connections to the Russians.”

In a series of strongly worded tweets, Warren said that Sessions must step down.

And we need Attorney General Jeff Sessions – who should have never been confirmed in the first place – to resign. We need it now. — Elizabeth Warren (@SenWarren) March 2, 2017

And in a statement, Rep. Elijah Cummings, D-Maryland, said, "Attorney General Sessions should resign immediately, and there is no longer any question that we need a truly independent commission to investigate this issue."

In a statement Wednesday night, Sessions replied to news of his two meetings with Sergei Kislyak, the Russian Ambassador to the U.S.: "I have never met with any Russian officials to discuss issues of the campaign. I have no idea what this allegation is about. It is false."

Sessions was asked during his confirmation hearings by Sen. Al Franken what he would do if he learned that "anyone affiliated with the Trump campaign communicated with the Russian government in the course of this campaign," Sessions replied:

"I have been called a surrogate at a time or two in that campaign, and I did not have communications with the Russians, and I'm unable to comment on it."

Sessions' spokeswoman, Sarah Isgur Flores, told NBC News that the then-senator did have a conversation with Kislyak last year but that "there was absolutely nothing misleading about his answer" at the hearing.

Flores told NBC News that Sessions was asked about "communications between Russia and the Trump campaign, not about meetings he took as a senator and a member of the Armed Services Committee," so "there was absolutely nothing misleading about his answer."

While some Democrats were calling on Sessions to resign, other lawmakers intensified demands that a special prosecutor be named to lead an investigation into ties between Russian officials and Trump campaign aides.

“This is even further proof of the need for an independent, bipartisan commission to investigate Russian interference with the 2016 election,” said Rep. Eric Swalwell, a Democratic member of the House Intelligence Committee.

Calls also mounted for Sessions to recuse himself from any investigation conducted by the FBI on the matter.

"If reports are accurate that Attorney General Sessions — a prominent surrogate for Donald Trump — met with Ambassador Kislyak during the campaign, and failed to disclose this fact during his confirmation, it is essential that he recuse himself from any role in the investigation of Trump campaign ties to the Russians," said Rep. Adam Schiff, top Democrat on the House Intelligence Committee.

"This is not even a close call; it is a must," Schiff added.