German and Spanish lawmakers protested against Julian Assange's detention on Monday, gathering outside a London prison to urge Britain and the EU to prevent his extradition to the United States.

Two far-left German MPs, Heike Hansel and Sevim Dagdelen of Die Linke, and a Spanish Green member of the European Parliament, Ana Miranda, had been due to meet their "friend" Assange in London's Ecuadoran embassy later on Monday.

Belmarsh prison is often used to hold high-profile suspects deemed to pose a threat to UK national security / © AFP/File

Instead, following his expulsion and arrest last week, they protested outside the top-security Belmarsh prison in southeast London where he is being held, carrying placards demanding his release.

"We are faced with a humanitarian imperative now that Assange is in UK custody and a US extradition request is out for him, after high ranking officials of the US -- including President Donald Trump -- have threatened the publisher with death," said Miranda.

The WikiLeaks founder is in custody awaiting sentencing for breaching his British bail conditions in 2012 by seeking refuge in Ecuador's London embassy to avoid extradition to Sweden.

Assange was arrested last week for breaching his bail conditions in 2012 by seeking refuge in the Ecuadoran embassy. The US has asked for his extradition / © AFP/File

He was arrested at the embassy on Thursday after Ecuador revoked his asylum, and is now also fighting a US extradition warrant relating to the release by WikiLeaks of a huge cache of official documents.

The US indictment charges Assange with "conspiracy" for working with former US Army intelligence analyst Chelsea Manning to crack a password stored on Department of Defence computers in March 2010.

Spanish European Parliament lawmaker Ana Miranda Paz says extraditing Assange to the US would set a "dangerous precedent" / © AFP

Extradition to the United States would set "a dangerous precedent" for journalists worldwide, said Miranda, adding: "this threatens to criminalise journalism globally."

- EU 'must take action' -

Dagdelen urged Britain and the EU to block any extradition request.

"We call on the British government not to extradite Julian Assange to the USA.

"The European Union must take action to protect a politically-persecuted publisher and journalist," said the German politician, calling on Spain and her home country to grant Assange asylum.

The lawmkaers -- Spanish MEP Ana Miranda Paz (L), and Germany's far-left MPs Sevim Dagdelen (C) and Heike Hansel (R) -- described Assange as a "good friend" / © AFP

The three women were trying to see Assange in prison, but their application was "still pending".

"I'm a friend of Julian Assange. He's a son, a father, a brother and a good friend," said Dagdelen.

"His whole life he sacrificed for the truth."

They also accused the Ecuadoran government of "engaging in a disinformation and slander campaign against Assange" after a series of reports emerged detailing his increasingly disfunctional relationship with embassy staff.

Belmarsh has frequently been used in high-profile national security cases, including that of former Finsbury Park Mosque hate preacher Abu Hamza, who now resides in a US "supermax" prison following extradition.

Assange is fighting the US extradition request / © AFP/File

Radical cleric Anjem Choudary, who was convicted in 2016 of encouraging support for the Islamic State group, spent some of his sentence there.

Belmarsh earned the moniker "the UK's Guantanamo Bay" in the period following the 9/11 attacks after it was used to detain a number of people under anti-terror laws.