US Senate minority leader Chuck Schumer has called on Attorney General Jeff Sessions to resign and for his reported meetings with the Russian ambassador to be investigated.
Mr Schumer said a special prosecutor should be appointed to conduct a probe into Russian involvement in the presidential election, and "to discover if the investigation has already been compromised" by Mr Sessions' own conduct.
US media reported on Wednesday night that Mr Sessions met with the Russian ambassador Sergey Kislyak twice during the campaign period, despite giving evidence seemingly to the contrary, under oath, during his confirmation hearing in January.
"His integrity and independence have been questioned, it would be better for the country if he resigns," Mr Schumer told a news conference.
The Democrat asked if Mr Trump knew about the meetings between Mr Sessions and the Russian ambassador when he appointed him Attorney General, and said an investigation also needed to establish whether Mr Sessions "disclosed these meetings during his FBI background checks".
Nancy Pelosi, the House minority leader, said that the fact Mr Sessions, as "the top cop in our country... lied under oath" was grounds for him to resign.
And she went a step further from her statement after the reports about Mr Sessions first emerged last night, joining Mr Schumer in calling for the Attorney General to himself be investigated.
The Justice Department insists there was "nothing misleading" about Mr Sessions statements to the Senate in January, when he was asked if he was aware of contacts between the Trump team and Russia.
Then, he said he was "unaware of those activities", before adding: "I have been called a surrogate at a time or two in that campaign and I didn't have, did not have communications with the Russians, and I'm unable to comment on it."
Justice Department spokeswoman Sarah Isgur Flores said "there was absolutely nothing misleading about his answer", saying he spoke to the ambassador only in his role as a member of the Senate Armed Forces committee.
At least three Republicans — Reps. Jason Chaffetz of Utah, Darrell Issa of California and Tom Cole of Oklahoma — have said they want Mr Sessions to withdraw from a inquiry Senate inquiry into Russia and the election.
The attorney general "is going to need to recuse himself at this point," Mr Chaffetz, chairman of the House Oversight and Government Reform Committee, told MSNBC.
Mr Sessions told the same network on Thursday: "I have said that, when it's appropriate, I will recuse myself."