Governments across the world began investigating possible financial wrongdoing by the rich and powerful on Monday following a leak of documents from a Panamanian law firm which allegedly showed how clients avoided tax or laundered money.

The documents detailed schemes involving an array of figures from friends of Russian President Vladimir Putin to relatives of the prime ministers of Britain, Iceland and Pakistan and as well as the president of Ukraine, journalists who received them said.

While the "Panama Papers" detail complex financial arrangements benefitting the world's elite, they do not necessarily mean the schemes were all illegal.

The Kremlin said the documents contained "nothing concrete and nothing new" while a spokesman for British Prime Minister David Cameron said his late father's reported links to an offshore company were a "private matter".

Iceland's Prime Minister Sigmundur Gunnlaugsson could not immediately be reached for comment on the naming of his wife in connection with a secretive company in an offshore haven which brought opposition calls for him to resign.

Pakistan denied any wrongdoing by the family of Prime Minister Prime Minister Nawaz Sharif after his daughter and son were linked to offshore companies. Ukrainian President Petro Poroshenko has not commented on his reported offshore links.

Opponents said Poroshenko should be impeached for allegedly transfering his confectionary business to an offshore company in 2014, amid fierce fighting between Ukraine and pro-Russian separatists. A senior official from the General Prosecutor's office said there was no evidence he had committed a crime.

Australia, New Zealand, India, France and Austria were among countries which said they had begun investigating the allegations, based on more than 11.5 million documents from law firm Mossack Fonseca, located in the tax haven of Panama. Banks as well as individual clients came under the spotlight.

The documents were leaked to the International Consortium of Investigative Journalists (ICIJ) and more than 100 other news organisations. Mossack Fonseca has denied any wrongdoing.

"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," ICJC director Gerard Ryle said.

ARMS AND DRUGS?

The material covers a period over almost 40 years, from 1977 until 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 Putin, including concert cellist Sergie Rolddugin. Reuters could not confirm those details.

Putin's spokesman dismissed the reports, saying they aimed to discredit him ahead of upcoming elections.

"This Putinophobia abroad has reached such a point that it is in fact taboo to say something good about Russia, or about any actions by Russia or any Russian achievements. But it's a must to say bad things, a lot of bad things, and when there's nothing to say, it must be concocted. This is evident to us."

The publications contained "nothing concrete and nothing new" about Putin, Kremlin spokesman Dmitry Peskov said.

The British government asked for a copy of the leaked data, which could be embarrassing for Prime Minister Cameron, who has spoken out against tax evasion and tax avoidance.

His late father, Ian Cameron, is mentioned in the files, alongside some members of his Conservative Party in the upper house of parliament, former Conservative lawmakers and party donors, British media said.

Jennie Granger, director general of enforcement and compliance at HM Revenue and Customs, said the government had a great deal of information from a wide range of sources.

"We will closely examine this data and will act on it swiftly and appropriately," she said.

Cameron's spokeswoman declined to comment on whether the leader's family had money invested in offshore funds set up by his father, saying it was a "private matter".

Tax authorities in Australia and New Zealand said they were probing local clients of Mossack Fonseca.

The Australian Tax Office said it was investigating more than 800 wealthy clients and had linked more than 120 of them to an associate offshore service provider located in Hong Kong, which it did not name.

DATABASE "HACK"

The head of Mossack Fonseca, Ramon Fonseca, has denied any wrongdoing but said his firm had suffered a successful but "limited" hack on its database. He described the hack and leak as "an international campaign against privacy".

Fonseca, who was up until March a senior government official in Panama, told Reuters that the firm, which specialises in setting up offshore companies, has formed more than 240,000 such companies, the "vast majority" used for "legitimate purposes".

The papers also showed the use of off-shore companies by Pakistini Prime Minister Nawaz Sharif's family, including his daughter Mariam and son Hussain. Pakistani Information Minister Pervez Rasheed denied any wrongdoing on their part.

"Every man has the right to do what he wants with his assets, to throw them in the sea, to sell them, or to establish a trust for them. There is no crime in this in Pakistani law or in international law," Rasheed said. - Reuters