WikiLeaks’ payment processor is preparing to sue credit card companies Visa and MasterCard over their refusal to process donations to the whistle-blowing website.

Andreas Fink, the CEO of Iceland’s DataCell, said he would seek damages from the US financial companies over their decision to block WikiLeaks funds.

“It’s difficult to believe that such a large company as Visa can make a political decision,” Mr Fink said in a telephone interview from Switzerland.

In an earlier statement, his company had defended WikiLeaks, saying “it is simply ridiculous to think WikiLeaks has done anything criminal”.

WikiLeaks has been under intense pressure since it began publishing some 250,000 US State Department cables, with attacks on its websites and threats against its founder, Julian Assange. He is in a British prison fighting extradition to Sweden over sex crime allegations.

A host of US internet and financial companies have severed their links to the controversial website, some citing breaches of their terms of use.

Earlier this week, Visa and MasterCard said they would stop processing payments to WikiLeaks but have not offered a detailed explanation of why. Supporters were outraged, with many noting organisations such as the American KKK and the British National Party both claim to accept Visa and MasterCard. MasterCard has declined repeated requests for comment. Visa Europe spokesman Simon Kleine said organisations could receive funds through Visa as long as they were legal and did not breach the company’s operating rules.

But he said when issues arose “we need to ensure that they’re in compliance with our operating rules and in compliance with local laws”.

He declined to say what the issues were in WikiLeaks’ case. “We investigate on a commercially confidential basis,” he said.

Mr Fink said he was officially told of the suspensions through Danish financial services company Teller, which runs part of the payment infrastructure. He said a team from Teller was on its way to Iceland to conduct what he described as “due diligence”.

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