Julian Assange believes comments made by the US president offer a “ray of hope” in his fight to avoid extradition.
President Joe Biden said he is “considering” dropping the prosecution of the Australian journalist.
Mr Biden’s reaction to a question at the White House came on Wednesday, the eve of the fifth anniversary of the WikiLeaks founder being held in Belmarsh prison in London.
Assange faces prosecution in the United States over an alleged conspiracy to obtain and disclose secret military and diplomatic files in 2010 relating to the wars in Afghanistan and Iraq.
Mr Biden said he was considering a request from the Australian government to drop the prosecution.
Australian prime minister Anthony Albanese has been pressing for Assange’s release for the past few months.
When asked about the request by reporters at the White House on Wednesday, President Biden replied: “We’re considering it.”
Assange was taken to Belmarsh prison five years ago, after being dragged out of the Ecuadorian embassy in London where he had stayed for seven years while trying to avoid extradition.
Kristinn Hrafnsson, editor-in-chief of WikiLeaks, visited Assange in prison on Thursday.
He told the PA news agency that the WikiLeaks founder believed Mr Biden’s comments were a “ray of hope” and a “positive step.”
But Mr Hrafnsson said more information was now needed to follow up on the remarks, adding: “We need to know if something serious is going on.
“We assume some process will now take place to find out what it entails.”
Mr Hrafnsson added that Assange is “not in a good mental state”, having suffered both “mentally and physically” after exposing the “truth”.
“Nobody would be in a good state after having spent five years inside with this very uncertain outcome about his life future, constantly angry,” he said.
“And this endless and tiresome process in the courtrooms here in London which are borderline becoming farcical.
“He’s not in a good state. He is resilient. And what keeps him alive is his family and the tremendous support on the outside.
“(Also) with the inner feeling that he did nothing wrong, he did – on the contrary – everything right.
“History will prove that and people are beginning to understand that you cannot criminalise journalism as we are seeing being done here.”
Asked about the potential re-election of Donald Trump as president, Mr Hrafnsson said he tries not to see “the fear of that outcome”.
“This is simply an opportunity for Biden to discontinue this legacy that he inherited from the previous administration, because the charges were brought about under Donald Trump.”
Agnes Callamard, Amnesty International secretary-general, said: “Julian Assange dared to bring to light revelations of alleged war crimes committed by the USA. It is unacceptable that years of his life have been stolen.
“The US authorities have failed to conduct a full and transparent investigation into their alleged war crimes.
“Instead, they have chosen to target Assange for publishing information leaked to him – even if it was of public interest.
“The ongoing persecution of Assange makes a mockery of the USA’s obligations under international law, and their stated commitment to freedom of expression.
“If extradited to the USA, Assange will be at risk of serious abuse, including prolonged solitary confinement, which would violate the prohibition on torture or other ill-treatment.
“Dubious diplomatic assurances made by the USA as to his treatment are not worth the paper they are written on, not least because they are not legally binding and are riddled with loopholes.”
“The president has not answered any questions about Julian before so it’s clear he would not say this out of the blue.”