- Video report by ITV News Washington Correspondent Robert Moore
The Trump administration threatens to be derailed once again by fresh damaging allegations about its ties to Russia.
Attorney General Jeff Sessions twice spoke to the Russian ambassador to the United States during Donald Trump's presidential campaign last year.
This contradicts testimony Mr Sessions gave during his confirmation hearing to become attorney general on January 10.
"I did not have communications with the Russians," Mr Sessions said - under oath - when asked about alleged ties between the Trump campaign and the Kremlin.
Mr Sessions, a former senator from Alabama who was one of Mr Trump's earliest and most passionate supporters on the campaign trail, denied meeting with "any Russians at any time to discuss any political campaign" in an interview with NBC on Thursday.
He said any suggestion he colluded with Russian officials during the presidential campaign were "unbelievable to me and are false".
As attorney general, Mr Sessions oversees the FBI which is currently investigating Russia's meddling in the 2016 election and any possible links to associates of Trump.
Asked whether he would distance himself from any investigation into communications between the Trump campaign and Russia, Mr Sessions said: "I have said whenever it's appropriate, I will recuse myself - there's no doubt about that."
Leading Democrats, including Chuck Schumer, Nancy Pelosi and Elizabeth Warren, have called for Mr Sessions' immediate resignation, accusing him of lying under oath.
"For the good of the country, Attorney General Sessions must resign," Mr Schumer said.
A growing number of Republicans are also now calling for Mr Sessions to recuse himself from any investigation into Russian interference and clarify his comments.
“If there is something there, and it goes up the chain of investigation, it is clear to me that Jeff Sessions, who is my dear friend, cannot make this decision about Trump,” Lindsey Graham said.
The accusations against his attorney general will be a blow to Mr Trump, who had been basking in praise from his colleagues and pundits for his address before Congress on Tuesday night.
The president has been dogged by questions about his administration's ties to Russia since winning the election.
The latest claims come just two weeks after he fired his national security adviser Michael Flynn after revelations emerged that he had discussed US sanctions with the Russian ambassador to the United States before the inauguration and then lied about the nature of the conversation with Vice President Mike Pence.
Mr Trump has consistently denied that his campaign had any contact with Russian officials, dismissing it as "fake news".
When asked at a press conference last month whether anybody from his campaign team had been in communication with Russia, Mr Trump replied: "Nobody that I know of."
But the controversy and suspicion has not disappeared.
Mr Trump's warm words towards Vladimir Putin and suggestion that the United States and Russia could form a closer relationship has left many in his own party uneasy.
"When it comes to Russia, he has a blind spot," Mr Graham said.