U.S. intelligence and defense officials have been ordered to preserve documents and emails that could be relevant to national security leak investigations being pursued by federal prosecutors, Obama administration officials said on Tuesday.

A U.S. defense official said the order to Defense Department personnel applies to any documentation - emails, faxes and paper documents - that might be relevant to investigators.

"We are in receipt of a preservation order issued by the Justice Department," the official said. Intelligence agency personnel have also been ordered to preserve records, Reuters reports.

A law enforcement official said that preservation orders are "routine procedures in leak investigations."

White House press secretary Jay Carney said he had no comment on whether White House officials were subject to a similar order. A Justice Department spokesman declined to comment. The FBI did not respond to an email requesting comment.

Reuters reported earlier this month that U.S. Attorney's offices in Baltimore and Washington were investigating two specific alleged leaks of classified information.

One leak involved a series of revelations in a book and article by a New York Times journalist about the alleged role of U.S. agencies in cyber-warfare activities against Iran. These included the creation and deployment of a virus known as Stuxnet which attacked Iranian uranium enrichment equipment.

The second leak under investigation by the U.S. attorneys relates to the publication by the Associated Press in May of a report disclosing the foiling of a plot by Yemen-based Al Qaeda in the Arabian Peninsula (AQAP) to attack an airliner using a newly designed underpants bomb.

Reuters reported that shortly after the AP published its report, White House counter-terrorism adviser John Brennan held a conference call with TV pundits in which he talked about how the U.S. had "inside control" over the underpants plot. Hours later, media began reporting what officials said was the biggest secret of the operation: that western spy agencies, led by the British, had control over the plot through an informant in AQAP.

U.S. officials said that despite widespread publicity, including a book by a Newsweek editor and a lengthy New York Times article, of what are ostensibly classified U.S. drone warfare campaigns in Pakistan, Yemen and Somalia, leaks related to drones are not part of the U.S. Attorneys' inquiries.

The main reason the drone leaks are not under scrutiny, officials said, was that administration officials, including Brennan and President Barack Obama, publicly talked about drone attacks, undermining the legal premise for any investigation.