Julian Assange has been blocked from seeing evidence in his extradition case as he battles against being sent to the US, a court has heard.

Lawyers representing the WikiLeaks founder told a hearing they were not being given sufficient access to their client in prison.

Mr Assange appeared at Westminster Magistrates' Court via a video link on Friday for the hearing, which was about extending his custody at HMP Belmarsh.

Defence lawyer Gareth Peirce said Mr Assange's legal team was struggling to prepare documents for the case because their client had no access to the evidence.

“Without Mr Assange's knowledge, some of it is recently acquired evidence, some of it is subject to months of investigation not always in this country, of which he is unaware because of the blockage in visits,” she said.

Key moments for Julian Assange Show all 9 1 /9 Key moments for Julian Assange Key moments for Julian Assange The situation today Assange was arrested after Metropolitan Police officers were invited into the Ecuadorian embassy on April 11 2019. How did it come to this? Ruptly TV Key moments for Julian Assange The break Assange shows the front page of the Guardian on July 26 2010, the day that they broke the story of the thousands of military files leaked by WikiLeaks AFP/Getty Key moments for Julian Assange Wanted A warrant for Assange's arrest was issued in August 2010 for counts of rape and molestation in Sweden AFP/Getty Key moments for Julian Assange Ruling The UK's Supreme Court ruled in 2012 that Assange should be extradited to Sweden to face trial Getty Key moments for Julian Assange Sanctuary Following the ruling, Assange was given asylum by the Ecuadorian governement over fears that his human rights would be violated if he were extradited, he has since remained in the embassy in London Getty Key moments for Julian Assange A friend in Pam Friend Pamela Anderson delivers lunch to Assange at the embassy in October 2016. She has since spoken against his arrest Getty Key moments for Julian Assange Arbitrarily detained A UN panel found in 2016 that Assange had been arbitrarily detained and that he had not been able to claim his full right to asylum. It urged Sweden to withdraw the charges against him Getty Key moments for Julian Assange The cat ultimatum Last year, the Ecuadorian embassy threatened to revoke Assange's internet access unless he stopped making political statements online and started taking better care of James, his pet cat. Assange accused Ecuador of violating his rights Reuters Key moments for Julian Assange Arrest Assange was arrested on April 11 2019. Ecuador revoked his asylum status and invited the Metropolitan Police in to the embassy to arrest him. Reuters

“Despite our best efforts, Mr Assange has not been given what he must be given, and we are doing our utmost to cut through this.”

Ms Peirce said the governor of HMP Belmarsh had prioritised family visits over legal visits and asked the judge to step in.

But the district judge Vanessa Baraitser said she had no jurisdiction over the prison service.

“I have no desire to stand in the way of any lawyer having proper access to their client and it's in the interest of justice that they do,” she said.

“What I can do and say is to state in open court that it would be helpful to this extradition process that Mr Assange's lawyers have the access to their client.”

Mr Assange is being held in prison ahead of a full hearing in February when he will fight extradition to the US.

He faces 18 charges, including conspiring to hack into a Pentagon computer.

Mr Assange is accused of working with former US army intelligence analyst Chelsea Manning to leak hundreds of thousands of classified documents.

With unkempt white hair and beard, he appeared uncomfortable as he sat waiting for the hearing to start, clenching his hands together before putting them inside the sleeves of his grey jumper.

Mr Assange was jailed in May for breaching bail conditions (AFP/Getty)

He spoke to confirm his name, date of birth, and nationality.

Mr Assange's lawyers have previously complained that he had been given access to an unsuitable computer in prison, while doctors have raised concerns over his health and fitness to stand trial.

Mr Assange has been in custody since he was dramatically removed from London’s Ecuadorian embassy in April. At a hearing in October, he appeared to struggle to say his own name, telling Westminster Magistrates' Court: “I can't think properly.”

He was jailed for 50 weeks in May for breaching his bail conditions by going into hiding to avoid extradition to Sweden over sex offence allegations in 2012.

Last month, Swedish authorities dropped their investigation into those allegations, which Mr Assange had denied.

He will next appear in court on Thursday for a case management hearing.