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A massive cache of leaked documents detail a shadowy network of banks and law firms that help many of the world's most powerful people — politicians, criminals, athletes, magnates, celebrities — hide money in offshore accounts, according to an coalition of investigative reporters.

The 11.5 million documents, said to be obtained by cryptic means, is larger than the trove of documents that have been published by WikiLeaks, and their release threw several countries into turmoil. Among the dozen current and former world leaders named in the documents as controlling offshore companies were the prime ministers of Iceland and Pakistan, the king of Saudi Arabia, and the children of the president of Azerbaijan, according to the International Consortium of Investigative Journalism, a nonprofit organization based in Washington that published the papers through more than 100 news organizations around the world on Sunday.

The group said they had also tied the movement of $2 billion by associates of Russian President Vladimir Putin, who countered that he was the victim of a smear campaign. The documents also link shell companies to Xi Jinping, head of China's ruling party, and to the late father of British Prime Minister David Cameron, both self-styled anti-corruption crusaders, the group said.

Some of the people and companies identified in the files are on United States blacklists for allegations of a variety of misdeeds, from consorting with terrorists, drug kingpins, or the rogue nations of Iran and North Korea, the journalists said.

The data, which originated with a law firm based in Panama called Mossack Fonseca, covers four decades of financial activity, through the end of 2015. It shows how dark money flows sub rosa through the international financial system, cheating governments from untold tax revenues and allowing crime of all types to flourish.

A Mossack Fonseca co-founder, Ramon Fonseca, confirmed the authenticity of the papers to Panama's Channel 2 television network. He said they had been stolen in a hacking attack.

The building where Mossack Fonseca is based in Panama City. CARLOS JASSO / Reuters

Fonseca said most of the people being named in news reports about big offshore accounts were not the firm's direct clients, saying the accounts were mainly established by financial intermediaries. He also said the firm did not engage in any wrongdoing. "We are not responsible for the actions of a corporation that we set up," he said in the TV interview.

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The firm said on its website that it had never been charged with a crime, and criticized media coverage for "mischaracterizations" and "misconceptions" about its work. It posted a detailed rebuttal to several of those reports.

Panamanian President Juan Carlos Varela issued a statement saying his government would cooperate "vigorously" with any judicial investigation arising from the leak of the law firm's documents.

The German newspaper Sueddeutsche Zeitung said it first received the data more than a year ago. The Munich-based daily was offered the data through an encrypted channel by an anonymous source who requested no monetary compensation and asked only for unspecified security measures, said Bastian Obermayer, a reporter for the paper.

ICIJ said the law firm's leaked internal files contain information on 214,488 offshore entities connected to people in more than 200 countries and territories. It said it would release the full list of companies and people linked to them early next month.

Icelandic PM Sigmundur David Gunnlaugsson JONATHAN NACKSTRAND / AFP - Getty Images

Iceland's prime minister, Sigmundur David Gunnlaugsson, was asked by Sweden's SVT television about a company called Wintris. He responded by insisting that its affairs are above board and calling the question "completely inappropriate," before breaking off the interview.

In Russia, the Kremlin last week said it was anticipating what it called an upcoming "information attack."

Putin's spokesman, Dmitry Peskov, told reporters that the Kremlin had received "a series of questions in a rude manner" from an organization that he said was trying to smear Putin, whose name did not appear in the documents.

"Journalists and members of other organizations have been actively trying to discredit Putin and this country's leadership," Peskov said.

The ICIJ said the documents included emails, financial spreadsheets, passports and corporate records detailing how powerful figures used banks, law firms and offshore shell companies to hide their assets. The data spanned a time frame of nearly 40 years, from 1977 through the end of 2015, it said.

Related: Tax Authorities Probe People Named in 'Panama Papers'

"It allows a never-before-seen view inside the offshore world — providing a day-to-day, decade-by-decade look at how dark money flows through the global financial system, breeding crime and stripping national treasuries of tax revenues," the ICIJ said.

Meanwhile, the British government asked on Monday for a copy of leaked data so it could act on any possible tax evasion.

The leak could be embarrassing for Prime Minister David Cameron. His late father, Ian Cameron, is mentioned alongside some members of his Conservative Party in the upper house of parliament, former Conservative lawmakers and party donors, British media reported.

When contacted by Reuters, Cameron's office declined to comment.

A U.S. Justice Department official told NBC News government lawyers are reviewing the documents for any potential violations of U.S. laws.

“We are aware of the reports and are reviewing them," the official said. "While we cannot comment on the specifics of these alleged documents, the U.S. Department of Justice takes very seriously all credible allegations of high level, foreign corruption that might have a link to the United States or the U.S. financial system.”