A company list showing the Mossack Fonseca law firm is pictured on a sign at the Arango Orillac Building in Panama City on April 3, 2016. Picture: Carlos Jasso

Berlin - A huge leak of 11.5 million documents from a Panama-based law firm reveals how top politicians, sports stars and criminals hide their money using offshore tax havens, Germany's Sueddeutsche Zeitung said on Sunday.

The leaked data link at least 12 current and former heads of state and 128 other politicians to illicit financial transactions. Those implicated include Russian President Vladimir Putin, former Egyptian autocrat Hosni Mubarak and Syrian President Bashar al-Assad.

The leak comes from Mossack Fonseca, one of the world's biggest and most secretive offshore law firms. The firm said it had never faced charges for criminal wrongdoing in its efforts to help clients launder money, dodge tax and circumvent financial sanctions.

The documents, dubbed the Panama Papers, were obtained by Sueddeutsche Zeitung, a daily newspaper headquartered in Munich. Sueddeutsche said an employee at the law firm had leaked the data, telling the newspaper he risked his life in doing so. The employee was not identified in the report.

The Panama Papers disclose the activities of 214 000 shell companies, according to the newspaper and other media from 78 countries that were involved in evaluating the data dump.

The newspaper also shared the Panama Papers with the Washington-based International Consortium of Investigative Journalists (ICIJ) and German state broadcaster ARD, the BBC and London-based newspaper The Guardian.

“2.6 terabytes of data, 11.5 millions documents, and 214 000 shell companies: The Panama Papers are the largest data leak journalists have ever worked with,” Sueddeutsche tweeted on Sunday.

According to ARD, the documents evaluated were emails, bank statements, copies of passports and other documents. In addition to laying open the offshore activities of 140 politicians and senior officials from around the world, the data include the names of spies, drug dealers and other criminals. Numerous celebrities and sports stars are also shown to have taken advantage of the services of the offshore companies.

The most widely circulated revelations from the Panama Papers shed light on the financial transactions that have contributed to the wealth of members of Putin's inner circle. The Guardian said that while Putin's name does not appear in any of the records, the data revealed a network of secret offshore deals and loans that formed a trail back to him and made his inner circle fabulously wealthy.

The BBC reported that the data reveal the existence of a money-laundering ring involving the Russian leader's closest associates and Bank Rossiya, a financial institution subjected to EU and US sanctions in the wake of Moscow's annexation of Crimea.

Georg Mascolo, who led the research for the Sueddeutsche Zeitung and two German broadcasters, said on Sunday evening on German television that he expected the insight into the business of tax havens to be quite “explosive”, adding that more revelations will come out.

The news which will be released by German media in the next few days “is very remarkable because we have not had such insight into the business of these tax havens on this scale”, Mascolo said.

German politicians with the country's left-leaning Social Democratic Party (SPD) and Green Party called for justice on the issue of tax evasion. Sven Giegold of the Green Party and a member of the European Parliament since 2009 called for more transparency.

“It is a shame that we are dependent upon such data leaks in the fight against miserable tax evasion,” Giegold said.

Edward Snowden, the US whistle-blower in the National Security Agency scandal, reacted by saying on Twitter that the biggest leak in the history of the data journalism was about corruption. Snowden, who fled the United States in 2013 after leaking information about the scope of the US government's data collection methods, highlighted revelations in the data linked to Iceland's prime minister.

Mossack Fonseca would not discuss specific cases of alleged wrongdoing, according to the media reports. It said it complies with anti-money-laundering laws and carries out thorough due diligence on all its clients.

Several media reports stressed that there are many legitimate uses of offshore companies, and that people can act make use of them while remaining legally and morally correct.

The Panamanian government issued a statement saying it followed a “zero tolerance” policy in all areas of the legal or financial services that are not handled with high levels of transparency.