One of the biggest document leaks in history snared world leaders, celebrities and sports stars in a snowballing worldwide scandal Monday over their secretive offshore financial dealings.

A year-long worldwide media investigation into a trove of 11.5 million documents, leaked from a Panama-based law firm with offices in 35 countries, exposed a tangle of confidential financial dealings by the elite, from aides of Russian President Vladimir Putin to relatives of Chinese President Xi Jinping, sports celebrities and screen stars.

The vast stash of records from legal firm Mossack Fonseca, the so-called Panama Papers, was obtained from an anonymous source by German daily Sueddeutsche Zeitung and shared with more than 100 media groups by the International Consortium of Investigative Journalists (ICIJ).

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

- Putin aides implicated -

Among the biggest findings of the media probe, which fingered about 140 political figures including 12 current or former heads of state:

-- Banks, companies and close associates of Putin, who is not himself named in the documents, "secretly shuffled as much as $2 billion through banks and shadow companies", according to the ICIJ. These allegations were not aired by Russian state TV.

-- The families of some of China's top communist brass -- including the nation's president -- used offshore tax havens to conceal their fortunes. At least eight current or former members of the Politburo Standing Committee, the ruling Communist Party's most powerful body, have been implicated.

-- A member of FIFA's ethics committee, Juan Pedro Damiani, had business ties with three men indicted in a corruption scandal. Argentine football great Lionel Messi and his father are named as owners of a Panama company, Mega Star Enterprises, that has not previously been disclosed in a Spanish tax probe into their affairs. UEFA chief Michel Platini used Mossack Fonseca to administer an offshore company, but he denied wrongdoing in a statement to AFP.

-- A Panamanian shell company may have helped hide millions of dollars from the Brink's-Mat heist, a $40 million British gold bullion robbery at London-Heathrow Airport in November 1983 that is etched in criminal folklore. The Panamanian law firm denies this allegations, however, the ICIJ said.

-- Iceland's Prime Minister Sigmundur David Gunnlaugsson secretly owned millions of dollars of bank bonds during his country's financial crisis when the country's financial system collapsed and banks had to be bailed out. The irritated premier denied wrongdoing in a television interview, which he cut short, but faces calls to resign and a no-confidence vote in parliament this week.

- Three of Pakistani Prime Minister Nawaz Sharif's four children -- Maryam, who has been tipped to be his political successor; Hasan and Hussain -- were named as owners of London real estate through offshore entities. But Sharif's son Hussain told Pakistani television: "There is nothing wrong with it and I have never concealed them, nor do I need to do that."

- 'Nothing wrong with it' -

The Panama Papers, from around 214,000 offshore entities covering almost 40 years, also name the president of Ukraine and the king of Saudi Arabia, as well as sporting and movie stars including Jackie Chan.

At least 33 people and companies listed in the documents were blacklisted by the US government for wrongdoing, including dealings with North Korea and Iran, as well as Lebanon's Islamist group Hezbollah, the ICIJ said.

President Francois Hollande promised Monday that French tax authorities will investigate the disclosures of the Panama Papers and that legal proceedings will follow. Australia said it, too, had launched a probe into 800 wealthy Mossack Fonseca clients.

"I think the leak will prove to be probably the biggest blow the offshore world has ever taken because of the extent of the documents," said ICIJ director Gerard Ryle.

One of the Panama law firm's founders, Ramon Fonseca, told AFP the leaks were "a crime, a felony" and "an attack on Panama".

"Certain countries don't like it that we are so competitive in attracting companies," he said.

Panama's government said it had "zero tolerance" for any shady deals, and vowed to "vigorously cooperate" with any legal investigations.

- 'Biggest leak in history' -

The massive leak of documents recalls Wikileaks' exploits of 2010 -- which included the release of secret military files and diplomatic cables.

However, in terms of size, "the 'Panama Papers' is likely the biggest leak of inside information in history," according to ICIJ.

More than 500 banks, their subsidiaries and branches have worked with Mossack Fonseca since the 1970s to help clients manage offshore companies. UBS set up more than 1,100 and HSBC and its affiliates created more than 2,300.

The documents show "banks, law firms and other offshore players often fail to follow legal requirements to make sure clients are not involved in criminal enterprises, tax dodging or political corruption," the ICIJ said.

Mossack Fonseca is already subject to investigations in Germany and Brazil, where it is part of a huge money laundering probe that has threatened to topple the current government.