Embattled US Supreme Court nominee Brett Kavanaugh may be edging closer to securing the top judicial role after two senators discredited an FBI report which detailed the sexual misconduct allegations levelled against him.

Republican senators, Jeff Flake and Susan Collins said the report to the Senate was unreliable because it failed to include the accounts of critical witnesses.

Their comments caused President Donald Trump’s fellow Republicans to feel reassured of Mr Kavanaugh’s chance at appointment.

Senator Collins said the FBI investigation appeared to be thorough while Senator Flake said he saw no additional corroborating information against Mr Kavanaugh, although he was “still reading” it.

This spurred thousands of anti-Kavanaugh demonstrators, including comedian Amy Schumer and model-friend Emily Ratajkowski, onto the steps of the Supreme Court to stop Mr Kavanaugh from securing the lifetime job on the top US court, but Republican leaders sounded unmoved.

“When the noise fades, when the uncorroborated mud washes away, what’s left is the distinguished nominee who stands before us,” Senate Majority Leader Mitch McConnell said on the Senate floor.

Protesters have demonstrated outside the Supreme Court following the report being finalised. Photo: AP/Manuel Balce Ceneta

Republicans will proceed with plans to vote to confirm the judge on Saturday.

Senator Flake was a key proponent of an investigation into the sexual assault claims raised by Christine Blasey Ford after describing her testimony as “compelling”.

In a post to Twitter, Mr Trump, himself accused by numerous women during the 2016 presidential race of sexual misconduct, said the completed FBI report showed the allegations against Mr Kavanaugh were “totally uncorroborated”.

Mr Trump can only risk losing the vote of one Republican If all Democrats reject Mr Kavanaugh’s nomination,

But as of yet, no Republican has indicated that they will vote against Mr Kavanaugh. Despite questioning the validity of the FBI report, Senators Flake and Collins did not explicitly announce their support for Mr Kavanaugh.

Democratic Senator Dianne Feinstein noted the FBI did not interview Mr Kavanaugh, who has denied the allegations, or Dr Ford.

“It smacks of a whitewash,” Democratic Senator Richard Blumenthal told reporters, saying the report should not give political cover for Republicans to vote for Mr Kavanaugh because “it is blatantly incomplete”.

Most Democrats opposed Mr Trump’s nomination of Mr Kavanaugh from the outset. If confirmed, he would deepen conservative control of the court.

The FBI report was not released to the public. Senators were allowed to read it behind closed doors without taking notes or making copies.

White House spokesman Raj Shah said the Trump administration was “fully confident” Mr Kavanaugh had the necessary support.

-With AAP