Henry Kyle Frese, 31, who was arrested in October, faces a maximum of 10 years in prison when he is sentenced in June, the Department of Justice said in a statement.

It detailed how Frese had leaked information to two unnamed journalists, one of whom he lived with, in 2018 and 2019.

One news outlet, which was also not named, published eight articles containing classified information.

Frese searched restricted government computer systems at least 30 times in 2018 for information to pass on verbally to the two journalists.

He also sent some secret information via private messages on social media, the Department of Justice said, citing court documents.

"He alerted our country's adversaries to sensitive national defense information, putting the nation's security at risk," Assistant Attorney General for National Security John Demers said.

"Disclosing such information for personal gain, or that of others, is not selfless or heroic, it is criminal."

The journalists involved appeared to work for CNBC and NBC News, according to US media.

CNBC, citing "sources with direct knowledge of US intelligence reports," reported in May 2018 that China had installed anti-ship cruise missiles and surface-to-air missile systems on the contested Spratly Islands.

Frese was a contractor with DIA from January 2017 to February 2018, and then a full-fledged DIA employee, with clearance ranging up to top secret level, officials said.

The DIA is the US military's intelligence service.