The continued imprisonment of WikiLeaks founder Julian Assange has damaged Britain's record on press freedom, the website's editor-in-chief Kristinn Hrafnsson said on Friday.

In January, a London judge refused to grant a US request for Assange's extradition, but also refused him bail until a US appeal against that verdict is heard.

"The fact that Julian is still in prison seriously undermines the United Kingdom's ability to proclaim that they are defenders of the freedom of the press all over the world," Hrafnsson told reporters.

Assange, a 49-year-old Australian, is wanted in Washington to face 18 charges relating to the 2010 release by WikiLeaks of 500,000 secret files detailing aspects of military campaigns in Afghanistan and Iraq.

The US claims he helped intelligence analyst Chelsea Manning steal the documents before exposing confidential sources around the world.

He faces a possible 175-year sentence if convicted, but Assange and his lawyers have long argued the case against him was politically motivated under former president Donald Trump.

Assange's supporters plan to highlight his continued incarceration with vigils on Sunday, to mark two years since he was taken to London's Belmarsh prison, and on Monday for World Press Freedom Day.

Jennifer Robinson, a member of Assange's legal team, said conditions in Belmarsh were "very difficult" and he remains "very isolated" after years of restrictions on his liberty.

"We are very concerned about his continued detention and consider it to be disproportionate," she added.

Both Robinson and Hrafnsson called on President Joe Biden's US administration to drop the charges, and for the Australian government to do more on Assange's behalf.

The Australian has been held at the high-security prison since he was convicted in 2019 for skipping bail, following his forcible removal from Ecuador's embassy in London where he had sheltered for seven years.