WikiLeaks founder Julian Assange stands on the balcony of the Ecuadorean Embassy in London in 2016. File picture: Frank Augstein/AP

London - The mother of WikiLeaks co-founder Julian Assange, who is fighting a bid to extradite him from Britain to the United States, appealed to British authorities on Friday to be "patient, gentle and kind" to her son.

Christine Assange also backed an online petition to free her 47-year-old son, highlighting long-term health concerns after he spent seven years inside the Ecuadorian embassy in London until police arrested him on Thursday.

She tweeted "a mother's plea to police, prison officers, court staff re my son Julian."

She said Australian citizen Assange had been "detained without charge" for eight years; deprived of fresh air, sunlight and exercise for six years; and spent three years "sick/in pain and denied proper medical/dental care."

"Please be patient, gentle and kind to him," she added.

The petition was launched by US actress Pamela Anderson, who befriended Assange during visits to him at the embassy.

Signed by 36,000 people, it urges the Australian government to help free Assange "before it's too late."

Assange, whose relationship with his hosts had become increasingly frayed, was dragged out of the embassy on Thursday morning after Quito revoked his asylum status and allowed police to enter the building.

The Metropolitan Police said he was arrested for skipping bail, adding later that he was "further arrested on behalf of the United States authorities."

The US Justice Department announced it has charged Assange for conspiring with former US military intelligence analyst Chelsea Manning to leak a trove of classified material in 2010.