Some 11m documents, known as the "Panama Papers’’ have been leaked from a Panamanian law firm, Mossack Fonseca.
Associates of Russian president Vladimir Putin are among those whose assets feature in the vast exposé published yesterday after a year-long investigation into 11m leaked documents.
Around 140 political figures are mentioned in the revelations, according to the probe by the International Consortium of Investigative Journalists (ICIJ).
The documents, which date back to 1975, show links to 72 current or former heads of state, including Middle East and North African dictators.
“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 Gerard Ryle, director of the ICIJ.
The leak contains secret offshore companies linked to the families and associates of Egypt’s former president Hosni Mubarak, Libya’s former leader Muammar Gaddafi, and current Syria president Bashar al-Assad.
It also revealed Icelandic prime minister Sigmundur Gunnlaugsson had an undeclared interest in his country’s bailed-out banks.
Leaked documents show Mr Gunnlaugsson and his wife, Anna Sigurlaug Pálsdóttir, bought offshore company Wintris in 2007. He did not declare his interest in the company when entering parliament in 2009, and sold his share of the company to Ms Pálsdóttir for a nominal sum eight months later.
Other files expose offshore companies controlled by the leaders of Pakistan, Saudi Arabia, and the children of the president of Azerbaijan.
The leak also reveals a suspected billion-dollar money laundering ring run by a Russian bank and involving close associates of Mr Putin.
The scheme was operated by Bank Rossiya, which is under US and EU sanctions.
Mossack Fonseca said it always carries out appropriate checks and regrets the alleged misuse of its services.
“For 40 years Mossack Fonseca has operated beyond reproach in our home country and in other jurisdictions where we have operations,” a spokesperson said. “Our firm has never been accused or charged in connection with criminal wrongdoing.
“If we detect suspicious activity or misconduct, we are quick to report it to the authorities. Similarly, when authorities approach us with evidence of possible misconduct, we always cooperate fully with them.”