WASHINGTON (Reuters) - Former intelligence contractor Edward Snowden began downloading documents describing the U.S. government's electronic spying programs while he was working for Dell Inc in April 2012, almost a year earlier than previously reported, according to U.S. officials and other sources familiar with the matter.

Snowden, who was granted a year's asylum by Russia on August 1, worked for Dell from 2009 until earlier this year, assigned as a contractor to U.S. National Security Agency facilities in the United States and Japan.

Snowden downloaded information while employed by Dell about eavesdropping programs run by the NSA and Britain's Government Communications Headquarters, and left an electronic footprint indicating when he accessed the documents, said the sources, speaking on condition of anonymity.

David Frink, a spokesman for Round Rock, Texas-based Dell, declined to comment on any aspect of Snowden's employment with the company, saying Dell's "customer" - presumably the NSA - had asked Dell not to talk publicly about him.

Since Snowden disclosed documents on previously secret U.S. internet and phone surveillance programs in June, his three-month tenure with U.S. contractor Booz Allen Hamilton Holding Corpstarting in late March of this year has been the focus of considerable attention. His time at Dell has received little attention.

Lawmakers have questioned how a relatively low-level systems administrator was able to gain access to so many top-secret documents without raising red flags. Some lawmakers have called the leaks one of the worst security breaches in U.S. history.

News that Snowden was downloading documents while he worked at Dell could increase pressure on U.S. intelligence agencies to tighten security protocols to prevent future leaks. The NSA has said it would tighten access to classified material and put in place stricter controls for accessing and downloading such information.

TRANSOCEANIC CABLES

Some of the material Snowden downloaded in April 2012 while a Dell employee related to NSA collection from fiber-optic cables, including transoceanic cables, of large quantities of internet traffic and other communications, the sources said.

Snowden has said he left Dell for a job at Booz Allen Hamilton in Hawaii around March of this year, specifically to gain access to additional top-secret documents that could be leaked to the media.

Booz Allen Hamilton fired Snowden after he fled to Hong Kong with a trove of secret material. The company has said it is cooperating with a number of inquiries into Snowden's hiring and security lapses.

It is not clear whether Dell has taken similar steps.

"We are honoring our customer's request that we not comment on this matter," said Frink, the Dell spokesman.

Two U.S. officials said the investigations into Snowden's activities confirmed that his downloading of sensitive information began at Dell. He is believed to have moved from Dell to Booz Allen with little time off in between.

In February 2010, while working for Dell, Snowden wrote in an internet technology forum, Ars Technica, that he was bothered by technology companies allegedly giving the U.S. government access to private computer servers.

"It really concerns me how little this sort of corporate behavior bothers those outside of technology circles," Snowden wrote under the screen name "The True HooHA." "Society really seems to have developed an unquestioning obedience towards spooky types.

In addition to a Justice Department investigation, which has produced criminal charges against Snowden, U.S. intelligence agencies are conducting an extensive inquiry to determine precisely what documents Snowden had access to, what he downloaded and how much damage his actions have caused.

(Reporting By Mark Hosenball; Editing by Tiffany Wu and Will Dunham)