Pressure is mounting on US Attorney General Jeff Sessions after it emerged that he met Russia's ambassador to Washington during last year's election campaign, seemingly contradicting statements he made in Senate confirmation hearings.

The revelation plunged President Donald Trump's Republican administration back into turmoil over its connections to Russia, which US intelligence says interfered in the 2016 campaign against Democratic candidate Hillary Clinton.

The Washington Post reported late on Wednesday that Sessions, a former senator who advised Trump's campaign on foreign policy and other issues, met Ambassador Sergey Kislyak in July and September, just as accusations of Russian interference in the election were building.

READ MORE: US House panel to probe alleged Trump-Russia links

Sessions, however, told his confirmation hearing at the Senate Judiciary Committee on January 10 that he did not know of contacts between Trump campaign members and Russia.

"I did not have communications with the Russians," he said under oath.

The previously undisclosed meeting fed growing calls for Sessions to recuse himself from oversight of justice department and FBI probes into the alleged Russian meddling and contacts with Trump campaign advisers.

"I have said whenever it's appropriate, I will recuse myself. There's no doubt about that," Sessions told NBC News, while denying any wrongdoing.

"I have not met with any Russians at any time to discuss any political campaign, and those remarks are unbelievable to me and are false. And I don't have anything else to say about that."

Republicans' reaction

The White House confirmed that the meetings took place but insisted Sessions had done nothing wrong as it dismissed the revelations as a partisan attack.

Trump on Thursday declared "total" confidence in Sessions, telling reporters during a visit to a US aircraft carrier that he "wasn't aware" of the two meetings last year.

But several leading Republicans joined Democrats on Thursday in calling on Sessions to step aside from the inquiry.

"AG Sessions should clarify his testimony and recuse himself," Jason Chaffetz, a member of the House Government Oversight Committee, said in a post on Twitter.

House Majority Leader Kevin McCarthy, said he thought Sessions "needs to clarify what these meetings were".

He said it was not unusual for members of Congress to meet ambassadors, but added that if a question arose about the integrity of a federal investigation, "I think it'd be easier" for an attorney general to step away.

'Resign immediately'

Top Democrats demanded that Sessions go further and quit his post as attorney general, calling for an independent, bipartisan investigation into Trump's possible ties to Russians.

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

US Representative Elijah Cummings criticised Sessions for keeping his contact with the ambassador secret even after Trump fired his first national security adviser, Michael Flynn.

Sessions "should resign immediately", he said.

House Speaker Paul Ryan said Sessions should only recuse himself if he is a subject of the probe.

At his Judiciary Committee confirmation hearing in January, Sessions was asked by Democratic Senator Al Franken what he would do if he learned of any evidence that anyone affiliated with the Trump campaign communicated with the Russian government in the course of the 2016 campaign, the Post reported.

"I'm not aware of any of those activities," Sessions responded, according to the Post.

He added: "I have been called a surrogate at a time or two in that campaign and I did not have communications with the Russians."

READ MORE: US Senate approves Jeff Sessions as attorney general

Speaking to Al Jazeera from Washington, DC, former associate US attorney general Bruce Fein said: "Everyone knows Jeff Sessions was up to his ears in the Trump campaign, that's why he's attorney general now."

He said that Trump has made powerful enemies so far in his presidency, including the press, that were "out to get him".

"And there are many people in the intelligence community that are probably out to get Mr Trump too because he's derided them, [accused] them of doing things equivalent to the Nazis. So he's going to have an intelligence community that's looking for things," Fein added.