WikiLeaks founder Julian Assange has denounced the firms that suspended payments to his website as instruments of U.S. foreign policy and called for help in protecting his work from their illegal and immoral attacks.

Ahead of a London court hearing on Tuesday at which Assange's lawyers will try to win his release on bail, he remained defiant, telling his mother from a British prison cell that he was committed to publishing more secret U.S. cables.

The 39-year-old Australian, whose website has provoked U.S. fury by publishing some of a trove of 250,000 classified U.S. diplomatic papers, is being held on allegations of sex crimes in Sweden, which he denies.

My convictions are unfaltering. I remain true to the ideals I have expressed. This circumstance shall not shake them, Assange said, according to a written statement of his comments supplied to Australia's Network Seven by his mother Christine.

We now know that Visa, Mastercard, Paypal and others are instruments of U.S. foreign policy, he said. I am calling for the world to protect my work and my people from these illegal and immoral attacks.

Assange handed himself in to British police last week after Sweden issued a European arrest warrant.

He has rejected the allegations of sexual misconduct by two female Swedish WikiLeaks volunteers and opposes attempts by Swedish authorities to extradite him for questioning.

His lawyers are due to return to court in London later on Tuesday to make a new application for bail after Assange was remanded in custody at an initial hearing last week.

OPERATION PAYBACK

Internet activists launched Operation Payback last week to avenge WikiLeaks against those perceived to have obstructed its operations, temporarily bringing down the websites of credit card firms Visa and MasterCard, as well as that of the Swedish government.

Assange's British lawyer, Mark Stephens, suggested however that Assange disagreed with the cyber attacks.

When I told Julian about the cyber attacks ... he said 'Look, I've been subject to cyber attacks. I believe in free speech, I don't believe in censorship and of course cyber attacks are just that', he told Sky News on Tuesday.

Stephens said Assange was on twenty-three-and-a-half hour lockdown in prison.

He is in isolation. He doesn't have access to newspapers or television or other news devices. He is not getting mail, he is subject to the pettiest forms of censorship, he said, adding that he expected a decision on bail by 1600 GMT.

Assange and his lawyers have voiced fears that U.S. prosecutors may be preparing to indict him for espionage over WikiLeaks' publication of the documents, which have embarrassed the United States and other countries.

The U.S. Justice Department has been looking into a range of criminal charges, including violations of the 1917 Espionage Act, that could be filed in the WikiLeaks case.

A ComRes poll of 2,000 Britons for CNN, published on Tuesday, found 44 percent believed that the sex allegations against Assange were an excuse to get him into custody so the United States could prosecute him for releasing the secret papers. The same proportion believed Britain should send Assange to Sweden to face questioning.

(Additional reporting by Michael Perry; Editing by Noah Barkin)

Australia United kingdom Wikileaks Julian Assange