Elected leaders and top officials from around the world are responding with denials and outrage to allegations that they used secret offshore companies and accounts to hide billions of dollars.

The media reports, based on a massive leak of documents, allege the existence of a clandestine network involving associates of Russian President Vladimir Putin, and business ties between a member of FIFA's ethics committee and men indicted for corruption.

The Kremlin has dismissed the allegations as "a series of fibs" aimed at discrediting Putin ahead of elections, while the FIFA official has described them as "ridiculous" and "outrageous." But some governments are acting on the information -- the U.K., France, Australia and Mexico have pledged to investigate for possible cases of tax evasion.

Several news organizations published reports Sunday drawing on more than 11 million documents leaked from a law firm in Panama that allegedly helped set up secret shell companies and offshore accounts.

The documents go back decades and reference 12 current or former world leaders, as well as 128 other politicians and public officials, according to the International Consortium of Investigative Journalists, which carried out the yearlong investigation in cooperation with more than 100 different news organizations.

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CNN hasn't been able to independently verify the reports and is seeking comment from the most prominent figures mentioned in the reports. Those people are spread across Europe, Asia, the Middle East, Africa and the Americas.

The documents do not necessarily indicate illegal activity. But shell companies and offshore accounts can be used to mask the origin of financial transactions and ownership. The files include people and companies blacklisted by the U.S. government because of links to drug trafficking and terrorism, according to the ICIJ.

They also suggest that the law firm in Panama, Mossack Fonseca, did not have adequate controls in place. According to the ICIJ, a 2015 internal audit found that the firm knew the identities of the real owners of just 204 of 14,086 companies it had incorporated in Seychelles, an Indian Ocean archipelago often described as a tax haven.

Ramon Fonseca Mora, a co-founder of Mossack Fonseca, told CNN late Sunday that the information published about the firm was false and full of inaccuracies.

In longer statements provided to the ICIJ, the firm said that the parties "in many of the circumstances" cited by the ICIJ "are not and have never been clients of Mossack Fonseca."

It said its role was to incorporate companies and that in 40 years, it had "never been accused or charged in connection with criminal wrongdoing."

A German newspaper, Suddeutsche Zeitung, obtained the files from an anonymous source and shared them with the ICIJ. Eventually, more than 100 other media organizations became involved, including the BBC, The Guardian, Univision and McClatchy.

Here are some of the most high-profile allegations from the reports:

RUSSIA

The reports say the leaked documents show the existence of "a clandestine network operated by Putin associates that has shuffled at least $2 billion through banks and offshore companies."

The files describe about 100 complex deals involving a network of Putin allies, including one where the rights to a $200 million loan were sold for just $1, according to the ICIJ. Putin isn't mentioned by name in any of the documents, the ICIJ notes.

Kremlin spokesman Dmitry Peskov anticipated the reports last week at a news conference, saying a media "attack" was expected in the coming days. He called the accusations "another series of fibs."

Speaking to state media on Monday, Peskov said the reports were the latest example of "Putinphobia."

"It's obvious that there are many journalists there whose main job isn't journalism," he was quoted as saying.

FIFA

Still reeling from an ethics crisis last year, FIFA is once again in the spotlight. The reports allege business ties between Juan Pedro Damiani, a member of its Independent Ethics Committee, and three men indicted on corruption charges by U.S. authorities.

The three men caught up in the FIFA corruption scandal are Eugenio Figueredo, a former FIFA vice president, and Hugo and Mariano Jinkis, a father and son who ran a sports marketing business in Argentina.

The leaked files show Damiani and his law firm did work for companies linked to Figueredo, the ICIJ reported. His law firm also served as an intermediary for a company linked to the Jinkis family, it said.

The report doesn't allege illegal behavior by Damiani, but it raises difficult questions for the embattled world soccer body that's trying to clean up its image.

Damiani, who is also the president of the Uruguayan soccer club Penarol, told a local TV station that the reports about him were "ridiculous" and "outrageous."

FIFA said it has begun a preliminary investigation to review the allegations.

ICELAND

The reports accuse the prime minister of Iceland, Sigmundur David Gunnlaugsson, of having ties, through his wife, to an offshore company that were not properly disclosed.

When asked about the company during an interview with a Swedish TV channel, Gunnlaugsson ended the conversation and said the journalists had asked an inappropriate question.

Among the firm's more significant holdings were bonds of three major Icelandic banks that collapsed in 2008, according to ICIJ. It said it was unclear how Gunnlaugsson's political activities might have affected the bonds' value.

In a statement later provided to ICIJ, the prime minister's office said the firm in question was merely a holding company for his wife's assets, enjoyed no tax advantages and had been created to avoid conflicts of interest in Iceland.

ARGENTINA

Argentinian President Mauricio Macri is alleged in the reports to have been a director of a company in the Bahamas that was incorporated in 1998 and dissolved in 2009. His father and brother were also reported to have been directors.

The ICIJ reports that he didn't disclose his link to the company in asset declarations in 2007 and 2008, a time when he was mayor of Buenos Aires.

A spokesman for the president, Ivan Pavlosky, said in a statement that Macri never had a stake in the company.

"President Macri didn't list that asset on his affidavit because he had no capital participation in the company and never had shares in it and therefore he didn't need to include it," he said.

Macri was "appointed occasionally as a director" of the company because it was "linked to the family business group," the spokesman said.

-- Charles Riley, Laura Perez Maestro, Euan McKirdy, Elizabeth Gonzalez and Alla Eshchenko contributed to this report.