PANAMA CITY (AFP) - Russian President Vladimir Putin denied any "element of corruption" on Thursday after a massive leak of confidential papers linked a close friend to a hidden US$2 billion (S$2.7 billion) offshore empire, and he blamed the United States for orchestrating the scandal.

Putin boasted that a year-long international media probe into the leak of 11.5 million offshore financial documents from Panamanian law firm Mossack Fonseca - the Panama Papers - had failed to find any mention of his name.

"They combed through these offshore accounts. Your humble servant is not there. What is there to talk about?" Putin said, referring to himself, at a televised forum for regional media held in Saint Petersburg.

Instead, the investigating journalists found "some friend of the Russian president" and suggested his activities have "an element of corruption," Putin said.

"What element of corruption? There is none at all," he insisted.

The probe into financial dealings by world leaders, celebrities and sports stars found that Putin's associates, notably his cellist friend Sergei Roldugin, "secretly shuffled as much as US$2 billion through banks and shadow companies," according to the International Consortium of Investigative Journalists (ICIJ).

The ICIJ coordinated the investigation with more than 100 media groups around the world after the mass of leaked data was obtained from an anonymous source by German daily Sueddeutsche Zeitung.

But "WikiLeaks has shown us now the fact that officials and official organs of the United States stand behind this," Putin said, after the whistleblowing group wrote on Twitter that "US govt funded #PanamaPapers attack story on Putin via USAID."

Putin warmly defended his friend as a "brilliant musician" and philanthropist.

Roldugin is a minority shareholder "in one of our companies," Putin said, apparently referring to Bank Rossiya where the cellist is a shareholder, adding that his earnings were wildly exaggerated by the reports.

"He earns some money there, not billions of dollars of course. That's rubbish, nothing of the sort," Putin said.

"Almost all the money he earned he spent on buying musical instruments abroad and brought them to Russia" to donate to state musical institutions, Putin said.

Panama is fighting off a feared international crackdown following the revelations of its role in secretive financial dealings, which have toppled Iceland's prime minister, led to a Swiss police raid on the headquarters of European football body Uefa, and prompted media allegations against the inner circles of both the Russian and Chinese presidents.

Faced by accusations that Panama has allowed the rich and powerful to hide their funds from international tax authorities and the law, President Juan Carlos Varela vowed to "confront whoever comes to put down Panama's image".

"I call on the OECD countries to return to the table for dialogue and seek agreements, and to not use these events to affect Panama's image," said Varela, whose country depends on the finance sector for seven percent of its economic output.

There was no immediate reaction to Varela's comment from the Paris-based, 34-nation Organisation for Economic Cooperation and Development, which helps to coordinate the global fight against tax evasion.

The Panama Papers put the embattled world of football back in the spotlight, too.

On Wednesday, Swiss police searched Uefa's Geneva offices as part of a probe into a Champions League television rights deal signed by Gianni Infantino before he became the president of world football's governing body.

The Panama Papers purportedly showed that Infantino had signed TV rights contracts for the Champions League with a company headed by two defendants later caught up in a corruption scandal.

Infantino, who was Uefa's legal director at the time he did the deals for the 2006 and 2007 tournaments with Argentinian TV rights specialists Hugo and Mariano Jinkis, told AFP he was "dismayed" by the claims and denied any wrongdoing.

The Panama Papers, which come from around 214,000 offshore entities and cover almost 40 years, claimed another scalp Wednesday when Uruguayan Juan Pedro Damiani resigned as an ethics judge for world football body Fifa after he was also named in the leaks.

Piling further pressure on Fifa, already reeling from a vast bribery scandal, Uruguayan Juan Pedro Damiani resigned as an ethics judge after he was linked in the papers to another disgraced football official wanted in the United States.

In Iceland, authorities called elections in the autumn and appointed agriculture minister Sigurdur Ingi Johannsson as premier after his predecessor was forced out over allegations he hid millions of dollars of investments in the country's banks.

Sigmundur David Gunnlaugsson was the first political scalp of what is thought to be the biggest ever leak of inside information in history.

Though not illegal in themselves, offshore financial transactions may be used to hide assets from tax authorities, launder the proceeds of criminal activities or conceal misappropriated or politically inconvenient wealth.

Investigators around the world, including in Australia, the Netherlands, El Salvador and Costa Rica, have all announced probes following the leak. A judicial source said Spain had opened a money-laundering probe into the law firm.

Many of the world's top banks have also been named in the leaks, including HSBC, UBS, Credit Suisse and Societe Generale, as creating thousands of offshore companies.