Julian Assange's mother has said she handed evidence to Ecuador's government indicating Washington wants to extradite her son to the United States.
She said on Monday she fears the WikiLeaks founder could face execution if extradited.
Assange has been staying in Ecuador's embassy in London for nearly six weeks as he awaits a decision on his asylum request by the leftist government of Rafael Correa.
The Australian anti-secrecy campaigner, who antagonised Washington in 2010 when his WikiLeaks website published secret US diplomatic cables, is wanted for questioning in Sweden over sex-crime allegations. He fears that if he is sent to Sweden he could be bundled off to the United States.
At a news conference after a meeting with Ecuador's Foreign Minister, Ricardo Patino, Christine Assange did not say exactly what evidence she had provided to substantiate her fears.
She said she had made the case for her son's asylum request and relayed her fears that the WikiLeaks founder could face torture and even execution if deported to the US.
"As a mother I'm terrified for what would happen to my son if he's extradited to the United States," she said, fighting back tears as she held pictures of her son as a toddler.
Christine Assange said she fears her 41-year-old son will not receive fair treatment in Sweden. Her biggest concern, she said, is that Sweden will extradite him to the United States.
"He'll then go to the United States, where he'll be possibly executed or perhaps tortured in a prison and will not face a hearing as we've seen with Bradley Manning," she said, referring to the US intelligence analyst charged with leaking classified government cables to WikiLeaks.
Patino said that, out of respect for the United Kingdom, his government will await the end of the Olympic Games in London to announce a decision on Assange's asylum application.
Swedish prosecutors still want to question him about allegations of rape and sexual assault made by two WikiLeaks supporters in 2010.
Assange, whose distinctive platinum hair and high-flying friends have made him a global celebrity, says he had consensual sex with the women.
Patino said Ecuador's ambassador in Sweden told Swedish authorities they are welcome to question Assange in the Ecuadorean embassy in London, which could give Assange a chance to fight the allegations without going to Sweden.