CAPE CANAVERAL, Florida (REUTERS) - Nasa has shut down access to an online database and banned new requests from Chinese and some other foreign nationals seeking access to its facilities amid mounting concerns about espionage and export control violations, the United States space agency's administrator said on Wednesday.

The security measures include a complete ban on remote computer access by Chinese and some other non-US contractors already working at Nasa centres, agency chief Charles Bolden said at a congressional oversight hearing in Washington.

The tightening of security follows the arrest on Saturday of Chinese national Bo Jiang, a former Nasa contractor. He was attempting to return to China with "a large amount of information technology that he may not have been entitled to possess", said Representative Frank Wolf, a Republican whose Virginia district includes the Nasa Langley Research Centre, where Jiang worked.

The Federal Bureau of Investigation arrested Jiang at Dulles International Airport outside Washington, where he had boarded a flight to Beijing, court papers provided by Mr Wolf's office show.

Jiang was arraigned on Monday at the US district court in Norfolk, Virginia. A detention hearing is scheduled for Thursday. He is charged with lying to federal law enforcement agents about computer hardware he planned to take with him to China, the court documents show.

Mr Wolf, who chairs the House Appropriations subcommittee on commerce, justice and science, identified Jiang last week during another hearing on possible security lapses at Nasa field centres.

"We know that China is an active, aggressive espionage threat," Mr Wolf, a longtime China critic, said during Wednesday's hearing.

"A recent White House report said that the technologies Nasa works on - aerospace and aeronautics - are those that the Chinese have most heavily targeted," he added.

Nasa is cooperating with federal investigators, in addition to conducting two internal reviews, Mr Bolden said.

The reviews are expected to be completed within a week, likely to be followed by an external investigation, Mr Bolden added.

In the interim, Nasa closed its Technical Reports database "while we review whether there is a risk of export control documents being made available on this website," Mr Bolden said.

Other security upgrades include a moratorium on granting any new access to Nasa facilities for individuals from China, Myanmar, Eritrea, Iran, North Korea, Saudi Arabia, Sudan and Uzbekistan. In addition, 281 foreign nationals, including 192 from China, who currently have access to Nasa facilities have had their remote computer access shut down.

"This is about national security, not about Nasa security, and I take that personally. I'm responsible and I will hold myself accountable once those reviews are completed," Mr Bolden said.