WikiLeaks founder Julian Assange married his long-term partner Stella Moris inside a British high-security prison on Wednesday at a small ceremony attended by just four guests, two official witnesses and two guards.

Assange is being held in jail while U.S. authorities seek his extradition to face trial on 18 counts relating to WikiLeaks' release of vast troves of confidential U.S. military records and diplomatic cables more than a decade ago.

"I am very happy and very sad. I love Julian with all my heart, and I wish he were here," Moris said outside the gates of Belmarsh prison following the ceremony.

The 50-year-old Australian, who denies any wrongdoing, has been in the southeast London jail since 2019, and before that was holed up in the Ecuadorean Embassy in the British capital for seven years.

While living at the embassy he fathered two children with Moris, a lawyer more than a decade his junior, whom he met in 2011 when she started work on his legal team. Their relationship began in 2015.

The registrar-led nuptials took place during visiting hours at the prison, where some of Britain's most notorious criminals have served sentences, including child murderer Ian Huntley. Afterwards, the guests were asked to leave immediately.

For the occasion, Moris wore a lilac satin wedding dress and Assange a kilt - a nod to his family ties to Scotland - which were created by British fashion designer Vivienne Westwood, who has campaigned against his extradition.

The bridal dress featured an inscription of a personal message from Westwood, and the long veil was embroidered with words such as "valiant", "relentless" and "free enduring love".

"To me, Julian is a pure soul and a freedom fighter," Westwood said.

Outside the jail, Moris cut a wedding cake and gave a speech to supporters who had gathered for the occasion.

"You know what we are going through is cruel and inhuman," she said. "The love that we have for each other carries us through this situation and any other that will come. He is the most amazing person in the world. He is wonderful and he should be free."

Assange suffered a blow earlier this month when he was denied permission to launch an appeal at Britain's Supreme Court against a decision to extradite him. However, he could still challenge the government's ratification of the extradition