Democrats say they remain unconvinced by Attorney General Jeff Sessions' latest comments regarding his contacts with the Russian ambassador in 2016.
House Democratic leader Nancy Pelosi is leading calls for America's top prosecutor to step down.
President Donald Trump said he was "an honest man" and described Democrats' pressure as "a total witch hunt".
Mr Sessions earlier removed himself from an FBI inquiry into alleged Russian meddling in the US election.
But he said he did not lie at January's confirmation hearing, when he said he had "no communications with the Russians".
He insisted his comments at his confirmation hearing were "honest and correct as I understood it at the time".
Mr Sessions was speaking after it had emerged that he met Russian ambassador Sergei Kislyak twice last year.
Mr Sessions was at the time a member of the Senate Armed Services Committee. But he was already a prominent member of Donald Trump's campaign team.
In a separate development on Thursday, a White House official said Mr Trump's son-in-law Jared Kushner and ousted National Security Adviser Michael Flynn met Mr Kislyak in December - after the 8 November election.
The official was speaking on the condition of anonymity.
Mr Flynn was fired last month after he misled the White House about his conversations with the Moscow diplomat, allegedly regarding US sanctions.
Claims of Kremlin interference have dogged President Trump.
In a series of tweets on Thursday, President Donald Trump defended Mr Sessions.Image copyright Twitter
But Mr Trump admitted that Mr Sessions "could have stated his response more accurately, but it was clearly not intentional".
'Simply not credible'
Ms Pelosi on Thursday repeated her call for Mr Sessions to quit.
She said his "his narrow recusal and sorry attempt to explain away his perjury" were totally inadequate.
Meanwhile, Adam Schiff, the top Democrat on the House intelligence committee, said Mr Sessions "clearly misled" the Senate and his explanation "is simply not credible".Media captionSenator Chuck Schumer: "Because the Department of Justice should be above reproach... [he] should resign"
Top Republicans in the House and Senate - including Senators Rob Portman, Marco Rubio and Lindsey Graham - earlier broke ranks to say Mr Sessions should recuse himself.
Crucially, though, senior Republicans have rallied behind him, and are also resisting demands for the appointment of an independent prosecutor, the BBC's North America correspondent Nick Bryant reports.
On Thursday, Mr Sessions categorically denied claims that he lied under oath at the confirmation hearing on 10 January about his contacts with Moscow.
During the January hearing Mr Sessions was asked: "If there is any evidence that anyone affiliated with the Trump campaign communicated with the Russian government, in the course of this campaign, what will you do?"
Mr Sessions responded: "I'm not aware of any of those activities. 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."
However, it has emerged Mr Sessions and Mr Kislyak held a private conversation in Mr Sessions' office in September and spoke at a meeting with several other envoys, on the sidelines of the Republican National Convention in July.
The former Alabama senator had meetings with more than 25 foreign ambassadors in the course of the year.Image copyright AP Image caption Russian envoy Sergei Kislyak was at the centre of the scandal that brought down Mike Flynn
Mr Sessions said he had spoken with the Russian ambassador as a US senator and not as Mr Trump's surrogate.
He said: "I never had meetings with Russian operatives or Russian intermediaries about the Trump campaign."
Mr Sessions said during the meeting with Mr Kislyak they talked about terrorism and then "somehow the subject of Ukraine came up".
For Mr Sessions to be charged with perjury, prosecutors would have to show that he not only made false statements, but knowingly and wilfully misled members of the committee about an indisputable fact.
The US intelligence community believes alleged Russian hacking of Democratic organisations in the election run-up was done to help Mr Trump defeat Hillary Clinton.
Mr Trump has branded suggestions that he or associates on his campaign had contact with Russian intelligence as "fake News".
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