The U.S. futures regulator has been investigating whether the CME Group did enough to safeguard customer money before the collapse of MF Global last year, sources said on Friday.

Sources familiar with the investigation into MF Global said the Commodity Futures Trading Commission is looking into the CME's supervision of customer money as a standard part of its review, which includes everyone involved from counterparties to affiliated creditors.

One source said there have not been any recent developments regarding the CME and that the CFTC has not changed or shifted its focus to the exchange, which served as MF Global's primary regulator.

"Investigators have never limited the scope of their inquiry to not include every entity or individual connected to the matter," said one source.

The New York Times on Thursday reported the CFTC had widened its inquiry to include the CME.

A spokeswoman for CME Group, the biggest operator of U.S. futures exchanges and MF Global's front-line regulator, said the company welcomed any probe.

"We haven't been notified that they are investigating us, but we would expect and frankly welcome it -- it's part of their job that they are looking at the things we did," CME spokeswoman Anita Liskey said. "We are confident that they will agree that we did our job to the best of our abilities."

MF Global filed for bankruptcy on Oct. 31 after it was forced to reveal that it had made a $6.3 billion bet on European sovereign debt, spooking investors and customers. MF Global Chief Executive Jon Corzine resigned a few days later.

James Giddens, the trustee liquidating MF Global's brokerage, has said a shortfall of customer funds could be as high as $1.2 billion, but other investigators say that figure is much lower. A diversion of customer funds for the benefit of the firm would be a violation of industry rules.

CME Executive Chairman Terrence Duffy has testified that MF Global provided false documentation to the CME about the customer funds under its control, saying it had a surplus and later correcting the documentation to show a deficit.

During a congressional hearing last month, Duffy said the CFTC declined to let the CME participate in its investigation of the collapse of MF Global. The government did not want duplicate efforts while federal investigators are conducting their review, said a source.

The CME has not been accused of any wrongdoing in connection with MF Global. Nor have its executives been charged.

Separately, the Wall Street Journal reported that former FBI Director Louis Freeh, the bankruptcy trustee for MF Global's parent company, has refused to turn over some documents to the CFTC.

Freeh asserted attorney-client privilege in deciding not to release certain documents to the CFTC, according to his office and people familiar with the matter, the Journal said.

The dispute is complicating efforts to learn how MF Global lost the customer funds and to return the money to its owners and could slow the investigation, the Journal said, citing people familiar with the investigation.

A spokesman for Freeh's office told Reuters that the trustee's team was cooperating with regulators, law enforcement and congressional committees and is not aware "that our initial desire to preserve the attorney-client privilege has hampered their respective investigations.

"To the extent that the authorities express concerns to us that the effort to preserve the attorney-client privilege is hampering their investigations, we of course would be willing to discuss the issue with them and be inclined to waive privilege," the spokesman said. (Reporting by Christopher Doering in Washington, Ann Saphir in Chicago, and Rachana Khanzode in Bangalore; Editing by Matt Driskill, Dave Zimmerman and Steve Orlofsky; rachana.khanzode@thomsonreuters.com; Within U.S. +1 646 223 8780; outside U.S. +91 80 4135 5800; Reuters Messaging: rachana.khanzode.thomsonreuters.com@reuters.net)