SYDNEY (AFP) - WikiLeaks founder Julian Assange has blasted top payment companies from behind bars for blocking donations to his website, saying he was determined to continue revealing government secrets.

Assange singled out three global giants which have stopped money sent to his website, credit card companies Visa and MasterCard and the Internet payment firm PayPal, in a statement from prison to Australian television Tuesday.

"We now know that Visa, MasterCard and PayPal are instruments of US foreign policy. It's not something we knew before," he said in a statement to Channel 7 dictated to his mother Christine Assange for the station.

"I am calling on the world to protect my work and my people from these illegal and immoral acts."

Assange said he was more determined than ever to publish thousands of sensitive documents on his whistleblowing website which has sent shockwaves around the world with the release of confidential US diplomatic cables.

"My convictions are unfaltering. I remain true to the ideals I have expressed," Australian-born Assange, 39, said in the brief statement.

"These circumstances shall not shake them. If anything, this process has increased my determination that they are true and correct."

Assange's mother has travelled to London to be with her son, where he is accused of sexual assault alleged to have taken place in Sweden.

While she was not able to see her son face-to-face, he spoke to her on the telephone for 10 minutes, telling her that he was being kept in a basement cell in solitary confinement.

It was the first time the pair had talked since the former hacker surrendered to British police on December 7 after Sweden issued a European warrant for his arrest so that he can be questioned on rape allegations.

Julian Assange also told his mother that prison surveillance cameras were monitoring his cell because of fears for his safety, Australia's Sunshine Coast Daily reported after speaking with Christine Assange in London.

WikiLeaks began the release of what is set to total some 250,000 US cables late last month, prompting condemnation from around the globe, including from the Australian government which has slammed the release as irresponsible.

In the wake of their release, Visa, MasterCard and PayPal suspended all payments to WikiLeaks earlier this month, prompting its supporters to knock offline the websites of credit card giants.

PayPal, which has said WikiLeaks was involved in activities deemed illegal by the US government, later said it would release all of the remaining funds in an account set up to raise money for the site but that it would no longer accept donations for WikiLeaks.

PayPal has said the decision to restrict the WikiLeaks account was not the result of any pressure from the US government.

Christine Assange said her son, who was due to face court again later Tuesday, had been heartened by the messages of support he had received.

"As a mother I am asking the world to stand up for my brave son," she told Channel 7.

Asked how she felt to finally speak with her son who has been one of the most famous people in the world in recent weeks, she said: "I can't put it into words. I'm connected back with him again. I've got the connection."