Federal law enforcement officials are mounting anti-espionage investigations at multiple NASA facilities to counter what FBI Director Robert Mueller believes is a growing threat against U.S. space technology.

"If anything, I would say that the threat is - is more substantial than perhaps it was 10, 15 years ago," Mueller said yesterday during a hearing of a subcommittee of the House Appropriations Committee that oversees both NASA and the FBI.

The subcommittee's chairman if Rep. Frank Wolf, R-VA.

Mueller told Wolf's panel that foreign nationals targeting NASA for espionage purposes are a "significant threat," and disclosed for the first time that the bureau has "a number of investigations ongoing" at several facilities within the space agency.

He declined to identify the NASA facilities involved or to say how many investigations are being conducted.

Mueller's comments followed the weekend arrest by FBI agents at Dulles Airport of Bo Jiang, a Chinese National who was trying to board a one-way flight to China.

Jiang was employed as a scientist by the National Institute for Aerospace, a contractor at NASA's Langley Research Center in Hampton, Va. Jiang was arraigned Tuesday in federal court.

The FBI is "investigating conspiracies and substantive violations of the Arms Export Control Act," according to the FBI's arrest warrant.

Jiang allegedly traveled to China in 2012 carrying "volumes" of sensitive NASA information. His position with NIA afforded him virtually unlimited, unescorted access throughout the Langley facility, which houses significant satellite technology resources with military applications.

Congressional sources say NIA paid Jiang at least $200,000 in income. The Chinese national remains in the custody of the U.S. Marshals Service pending a hearing scheduled for March 21 in U.S. federal court in Newport News, VA. He has a court appointed lawyer.

At Dulles airport, FBI agents found a number of electronic devices that Jiang attempted to conceal, including a laptop, an old hard drive and a SIM card.

Mueller told Wolf's panel that the FBI has not yet undertaken a "systematic review" of security throughout the space agency.

"I am not aware myself of a systematic review that's being done" of NASA research centers, Mueller said.

Wolf has long warned of espionage problems arising from the presence of foreign nationals working at NASA, especially those who like Jiang have access to NASA's Langley center and its Ames Research Center outside San Francisco.

Mueller also disclosed that for years the FBI has embedded agents at all 17 national labs operated by the U.S. Department of Energy, where nuclear missile research is undertaken.

He said he was unaware agents were permanently assigned in a similar way to safeguard NASA centers, although those facilities are instrumental for space defense research.

Richard Pollock is a member of The Washington Examiner's Watchdog investigative reporting team. He can be reached at rpollock@washingtonexaminer.com.