ZURICH (AFP) - Hackers claimed Wednesday to have attacked the websites of Mastercard and a Swiss bank in apparent reprisal for their decisions to choke off funding for the whistleblowing website WikiLeaks.

As WikiLeaks' founder Julian Assange spent his first full day in prison in London after he was refused bail on Wednesday, it emerged that one of Britain's highest-profile lawyers will fight moves to extradite him to Sweden to face rape accusations.

Assange's 20-year-old son meanwhile said he hoped his father's arrest in Britain was not a "step towards his extradition to the US."

WikiLeaks has enraged governments around the world by releasing a wave of US diplomatic cables, detailing everything from China's view of North Korea to unflattering descriptions of world leaders.

After WikiLeaks appealed for donations to be able to continue its activities, Mastercard and Visa said they were suspending payments to the site, apparently sparking attempts to hack into the sites.

A group of hackers dubbed Anon_Operation said they had brought down www.mastercard.com, although the company itself refused to comment.

The group, which claims it is fighting for "freedom on the internet", designated mastercard.com as their "current target" in what was rapidly taking the proportions of a cyber war.

The Swiss post office banking service, PostFinance, also confirmed its website was suffering "denial of service attacks" since it closed Assange's account on Monday.

Geoffrey Robertson, a barrister who has established a reputation for arguing for victims of human rights abuses, will defend Assange in his attempts to avoid extradition to Sweden where he faces allegations of rape and molestation.

After laying low for weeks, Assange emerged on Tuesday and handed himself in to police in London, appearing before a judge who denied him bail despite offers by celebrities, including film director Ken Loach, to put up surety.

He was ordered to return to court on December 14.

Assange's supporters insist the extradition request is politically motivated, a claim refuted by the lawyer for the two Swedish women behind the rape claims.

"There is absolutely no link between what those two women have been through and WikiLeaks, the CIA, or the American administration," Claes Borgstroem said.

The case "has nothing to do with WikiLeaks. I would like Julian Assange to come forward and say that himself," Borgstroem told reporters in Stockholm.

Assange's son Daniel, a software developer in the Australian city of Melbourne who has not been in contact with his father for a number of years, called for him to be treated justly following his arrest.

"Let us do our best to ensure my father is treated fairly and apolitically," he said on the Twitter microblogging site.

As WikiLeaks promised, it continued to release cables overnight Tuesday.

One revealed Washington had branded Australia's ex-premier Kevin Rudd as a "mistake-prone control freak" and another that the British government was relieved when its Scottish counterparts freed the Lockerbie bomber.

The dispatches from the US embassy in Tripoli showed Britain faced threats from Libya of "dire consequences" if Abdelbaset Ali Mohmet al-Megrahi -- who is suffering from cancer -- died in a Scottish prison.

A cable published by El Pais newspaper revealed that the Madrid government had offered to host the US military command for Africa (Africom) in southern Spain, near the port of Cadiz.

And there were also embarrassing revelations in connection with another US ally, Saudi Arabia, as cables painted a picture of a buzzing party scene inside princes' mansions in Jeddah replete with alcohol, drugs and sex.

In an op-ed piece for The Australian newspaper, Assange defended his site's decision to publish the treasure trove of 250,000 cables, believed to have been passed to WikiLeaks by a junior US soldier.

"The swirling storm around WikiLeaks today reinforces the need to defend the right of all media to reveal the truth," he wrote.