The Trump administration threatens to be derailed once again by fresh damaging allegations about its ties to Russia.

Attorney General Jeff Sessions allegedly spoke to the Russian ambassador on two occasions during Mr Trump's presidential campaign last year, according to the Washington Post.

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.

Leading Democrats, including Nancy Pelosi and Elizabeth Warren, have called for Mr Sessions' immediate resignation, accusing him of lying under oath.

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

Democrats are now demanding that Mr Sessions withdraw himself from the investigations and a special prosecutor be appointed to ensure a fully independent inquiry.

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.

The latest allegation has increased calls from Democrats and some Republicans for a special prosecutor to be appointed to ensure a fully independent probe.

Republican Senator Lindsay Graham, speaking at a CNN event on Wednesday, said Mr Sessions should distance himself from the FBI investigation and suggested a special prosecutor may now be needed.

"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," Mr Graham said.

Mr Sessions released a statement late on Wednesday, denying that he had ever discussed Mr Trump's campaign with Russian officials.

"I have no idea what this allegation is about - it is false," he said in a statement.

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.