Tax authorities worldwide are probing clients of a Panama-based law firm at the centre of a massive data leak for possible tax evasion.

The leak involves more than 11.5 million documents from the files of law firm Mossack Fonseca, based in the tax haven of Panama, revealing details of hundreds of thousands of clients in multiple jurisdictions.

The documents are at the center of an investigation published on Sunday by the International Consortium of Investigative Journalists, the German newspaper Süddeutsche Zeitung and more than 100 other news organizations around the globe. Suddeutsche Zeitung reported it received the huge cache of documents and then shared them with the other media outlets.

World leaders, sports stars, screen idols and dozens of billionaires were among those named in what looks to be the biggest ever leak of inside information in history.

The leaked "Panama Papers" cover a period over almost 40 years, from 1977 until as recently as last December, and allegedly show that some companies domiciled in tax havens were being used for suspected money laundering, arms and drug deals, and tax evasion.

Britain's Guardian newspaper said the documents showed a network of secret offshore deals and loans worth $2 billion led to close friends of Russian President Vladimir Putin. Reuters couldn't independently confirm those details.

Other top names include the world's best football player Lionel Messi; Iceland's Prime Minister Sigmundur David Gunnlaugsson and his wife, Bollywood's Amitabh Bachchan, his daughter-in-law actress Aishwarya Rai Bachchan, and martial arts movie star Jackie Chan.  The media adviser of the former Aishwarya Rai Bachchan has rejected the documents as "totally untrue and false".

The Australian Tax Office (ATO) said on Monday it is investigating more than 800 wealthy clients of Mossack Fonseca.

"Currently we have identified over 800 individual taxpayers and we have now linked over 120 of them to an associate offshore service provider located in Hong Kong," the Australian tax office said in a statement emailed to Reuters. It did not name the Hong Kong company.

DATABASE "HACK"

The head of Mossack Fonseca has denied any wrongdoing but acknowledged his firm had suffered a successful but "limited" hack on its database.

The firm's director, Ramon Fonseca described the hack and leak as "an international campaign against privacy".

Fonseca, who was up until March a senior government official in Panama, said in a telephone interview with Reuters on Sunday the firm, which specializes in setting up offshore companies, has formed more than 240,000 such companies and noted the "vast majority" of these have been used for "legitimate purposes."

ATO Deputy Commissioner Michael Cranston said his office was working with the Australian Federal Police, the Australian Crime Commission and anti-money laundering regulator Austrac to further cross-check the data from the documents.

"Some cases may be referred to the Serious Financial Crime Taskforce," Cranston said in the statement.

The 800 individuals under investigation include some taxpayers who had previously been investigated and others who had reported themselves to the tax office under a voluntary disclosure initiative, which allowed people to come forward and avoid steep penalties and criminal charges and has since ended.

However, the ATO said those under investigation also included a large number of taxpayers who had not previously come forward.

New Zealand's tax agency on Monday said it is "working closely" with its tax treaty partners to obtain full details of any New Zealand tax residents who may have been involved in arrangements facilitated by Mossack Fonseca.

John Nash, the New Zealand agency's international revenue strategy manager, told Reuters in emailed comments that there is an "active compliance programme focused on those who engage in abusive offshore arrangements and don't meet their tax obligations."

Separately, media reports said the leaked data pointed to a link between a member of global soccer body Fifa's ethics committee and a Uruguayan soccer official who was arrested last year as part of a wide-ranging US probe into corruption in the sport.

Fifa's ethics committee said in a statement on Sunday that Juan Pedro Damiani, a member of the committee's judgment chamber, was being investigated over a possible business relationship with fellow Uruguayan Eugenio Figueredo, one of the soccer officials arrested in Zurich last year.

Damiani told Reuters in Montevideo on Sunday that he broke off relations with Figueredo when the latter was accused of corruption. - Reuters and other sources