US federal prosecutors are conducting a criminal investigation into newspaper tycoon Conrad Black, it has been confirmed.
Lord Black has called the claims "unproven and untrue"
Lord Black, his former deputy David Radler and their company Hollinger Inc are already facing a civil lawsuit from the Securities and Exchange Commission.
They are accused of fraudulently taking $85m (£46m) from newspaper group Hollinger International.
The government said in court papers a criminal investigation was underway.
It was revealed on Tuesday that the US Attorney's office was trying to delay Lord Black's legal team from obtaining certain Security and Exchange Commission (SEC) documents related to the investigation, "to protect the integrity of the related criminal investigation".
The federal prosecutors want the release of the papers delayed until 1 August and have asked for a Wednesday court hearing in Chicago to achieve this.
Hollinger Inc's lawyer Nathan Eimer said his client wanted 150 boxes of documents from the SEC and did not know which ones the Attorney's office wants to block.
"We don't believe that the company has engaged in any criminal conduct," said Mr Eimer.
"We don't believe at the end of the day it will be found to have engaged in any criminal conduct."
The charges against Lord Black, his former deputy David Radler and Canadian company Hollinger Inc, relate to the period between 1994 and 2003.
They are accused of fraudulently taking $85m from US newspaper group Hollinger International, which they then controlled, for their own personal use.
Although Lord Black was forced to resign from Hollinger International in November 2003, he and his co-defendants continue to deny the charges.
Hollinger Inc, a holding company with a number of media and other assets, continues to owns 18% of Hollinger International.
In a separate pending civil lawsuit, Hollinger International claims Lord Black stole $380.6m to fund everything from a private jet to a Rolls-Royce and even payments to his butler.
Hollinger International owns the Chicago Sun-Times newspaper.
Last year it sold the Daily Telegraph in London and Israel's Jerusalem Post.