The Organization for Economic Cooperation and Development has said that Lebanon is among the countries that are refusing to “exchange information” after tax evasion probes were launched following a massive leak of confidential documents that lifted the lid on the murky offshore financial dealings of a slew of politicians and celebrities.

The scandal erupted on Sunday when media groups began revealing the results of a year-long investigation into a trove of 11.5 million documents from the Panamanian law firm Mossack Fonseca, which specializes in creating offshore shell companies.

Pascal Saint-Amans, head of tax policy at the OECD, said the leaks showed that Panama was among the world's shadiest tax havens.

"Among the countries that refuse to automatically exchange information, there are Bahrain, Nauru, Vanuatu and Lebanon," he told Agence France Presse.

"Switzerland is really making progress, so there is a concentration of problems in Panama," he said.

Offshore financial dealings are not illegal in themselves but may be used to hide assets from tax authorities, launder the proceeds of criminal activities or conceal misappropriated or politically inconvenient wealth.