Details claiming to reveal how little income tax US billionaires pay have been leaked to a news website.

ProPublica says it has seen the tax returns of some of the world’s richest people, including Jeff Bezos, Elon Musk, and Warren Buffett. The website alleges Amazon’s Mr. Bezos paid no tax in 2007 and 2011, while Tesla’s Mr. Musk paid nothing in 2018. A White House spokeswoman called the leak “illegal”, and the FBI and tax authorities are investigating.

ProPublica said it was analyzing what it called a “vast trove of Internal Revenue Service data” on the taxes of the billionaires and would release further details over the coming weeks.

While the BBC has not been able to confirm the claims, the alleged leak comes at a time of growing debate about the amount of tax paid by the wealthy and widening inequality. ProPublica said the richest 25 Americans pay less in tax – an average of 15.8% of adjusted gross income – than most mainstream US workers.

According to reports in the US, Michael Bloomberg, a former mayor of New York whose tax details were among the documents, said the disclosure raised privacy concerns and he would use “legal means” to uncover the source of the leak.

ProPublica, an investigative website, has written several articles about how budget cuts at the US Internal Revenue Service have hampered its ability to enforce tax rules on the wealthy and large corporations. The news organization said it received the leaked documents in response to these articles. White House Press Secretary Jen Psaki said that “any unauthorized disclosure of confidential government information” is illegal.

Treasury Department spokeswoman Lily Adams said in an emailed statement to Reuters that the matter has been referred to the FBI, federal prosecutors and two internal Treasury Department watchdogs, “all of whom have independent authority to investigate.”

US Internal Revenue Service Commissioner Charles Rettig said: “I can’t speak to anything with respect to specific taxpayers. I can confirm that there is an investigation, with respect to the allegations that the source of the information in that article came from the Internal Revenue Service.”

-BBC