The committee to investigate the lack of transparency in Panama's financial system itself lacks transparency, Nobel Prize-winning economist Joseph Stiglitz said on Friday after resigning from the Panama Papers commission.

The leak in April of more than 11.5 million documents from the Panamanian law firm Mossack Fonseca detailed financial information from offshore accounts and potential tax evasion by the rich and powerful.

Stiglitz and Swiss anti-corruption expert Mark Pieth joined a seven-member commission tasked with probing Panama's notoriously opaque financial system, but they say they found the government unwilling to back an open investigation.