A group of Internet activists calling themselves Operation Payback have taken credit for shutting down the website of a bank that earlier Monday froze funds belonging to WikiLeaks.

Announcing its successful hack on a Twitter account, the group declared, "We will fire at anyone that tries to censor WikiLeaks."

Earlier in the day, Swiss bank PostFinance issued a statement announcing that it had frozen 31,000 euro ($41,000 US) in an account set up as a legal defense fund for WikiLeaks founder Julian Assange.

The bank said it had frozen the account because, in opening it, Assange had claimed residency in Geneva.

"Assange cannot provide proof of residence in Switzerland and thus does not meet the criteria for a customer relationship with PostFinance," the bank said.

As of Monday evening, the PostFinance website was unavailable.

Operation Payback also promised a hack attack on PayPal, the online payment service that last week cut off WikiLeaks, denying the group a major tool for collecting donations from supporters.

With the financial noose tightening around WikiLeaks even as a legal one tightens around its founder's neck, Operation Payback has effectively declared war on the organizations working to hobble WikiLeaks.