WikiLeaks and the Icelandic IT company DataCell filed a formal complaint to the European Commission on Thursday, saying payment companies Visa Europe and MasterCard Inc violated EU antitrust laws by blocking donations.

Visa Europe, which runs the largest card network in the European Union, and MasterCard blocked WikiLeaks from using its network to collect funds from donors in December 2010.

The complaint, filed to the Directorate-General for Competition of the European Commission, says Visa and MasterCard breached antitrust provisions set out by Articles 101 and 102 of the EU Treaty.

DataCell, which has an agreement to collect credit card donations on behalf of WikiLeaks, says the credit card giants engaged in anti-competitive behavior and abused their dominant market position.

WikiLeaks, led by Australian Julian Assange, urged the EU Commission to order both credit card companies to lift their ban with immediate effect.

Visa and MasterCard stopped processing donations for WikiLeaks after the United States criticized the organization's release of sensitive diplomatic cables.

Visa said last December that it was investigating whether the nature of WikiLeaks' business contravened its operating rules.

Cyber hackers supporting WikiLeaks retaliated by attacking the Visa and Mastercard websites.

WikiLeaks has come under increased international scrutiny after releasing a slew of diplomatic cables that have embarrassed Washington.

Assange has also been subject to allegations of sexually assaulting two women in Sweden, which date from August, 2010. He appeared at the High Court in London this week to appeal against his extradition to Sweden to face the charges.

(Reporting by Stephen Mangan)