WikiLeaks editor-in-chief Kristinn Hrafnsson on Wednesday called for "a political solution" to the prosecution of Julian Assange, as supporters rallied in London to mark the fifth anniversary of his arrest there.

On Thursday, WikiLeaks founder Assange will have spent five years in the high-security Belmarsh Prison in southeast London, with Hrafnsson branding the jail term "so excessive and so brutal".

The 52-year-old Australian Assange is currently waiting to learn if he can make a last-ditch appeal against extradition to the United States, after a UK court last month delayed a decision on his case. It is now expected on May 20.

"This is a case that just should never have been started in the first place," Hrafnsson told AFP at the Wednesday afternoon rally in central London.

Other protests in support of Assange are expected around the world on Thursday.

"The solution to this case where we are dealing with a political persecution is a political solution and a political push," Hrafnsson said.

US President Joe Biden said Wednesday his administration was "considering" Australia's request to drop the prosecution.

Washington has spent several years trying to extradite Assange to face charges over Wikileaks' 2010 release of secret military and diplomatic files which related to the US-led wars in Iraq and Afghanistan.

Attempting to halt the process, Assange has suffered a string of court losses in the long-running legal saga, which his supporters see as a battle for media freedom.

Campaign groups including Amnesty International and Reporters Without Borders have called for his release and denounced the prosecution under the 1917 Espionage Act, which has never been used over the publishing of classified information.

Meanwhile Australia's parliament passed a motion in February with the prime minister's support calling for an end to the legal saga.

Hrafnsson said Canberra should "link" the case to its landmark AUKUS security pact with Washington and London, as well as possible trade agreements and future cooperation to secure Assange's release.

"They should be bold and say we have nothing to discuss unless you drop the charges against Julian Assange so he can walk free and come back to Australia," he said of the country's government