A US government watchdog is examining a contractor that conducted a 2011 background investigation into Edward Snowden, the source of recent leaks about US secret surveillance programmes.

Patrick McFarland, the inspector-general for the US Office of Personnel Management, told US legislators on Thursday that his office was investigating USIS, a Falls Church, Virginia-based company that is the largest private provider of federal government background checks.

The USIS investigation predates the Snowden scandal, but McFarland told the Homeland Security Subcommittee hearing that there are now concerns that USIS may not have carried out its background check into the 29-year-old Snowden in an appropriate or thorough manner.

Snowden had a Top Secret/Sensitive Compartmented Information level clearance.

The hearing helped underscore questions legislators have about the widespread use of contractors in sensitive intelligence work and the oversight of those employees.

Not only is much intelligence work handled by contractors, but private contractors also conduct roughly 75 percent of federal government background checks, according to legislators.

Snowden, who disclosed details of the US government's vast phone and internet surveillance, was a contractor formerly employed by Booz Allen Hamilton who worked at a National Security Agency (NSA) facility in Hawaii.

'Some problems'

USIS conducts federal employee background checks for the Office of Personnel management, the government agency primarily responsible for overseeing such investigations.

"Yes, we do believe that there - there may be some problems," McFarland said of Snowden's review.

USIS said in a statement that it has never been informed that it is under "criminal investigation".

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It said it received a subpoena for records from McFarland's office in January 2012.

"USIS complied with that subpoena and has cooperated fully with the government's civil investigative efforts," the statement said.

Regarding Snowden, USIS said it does not comment on confidential background investigations.

Meanwhile, according to top-secret documents published on Thursday by Britain's Guardian newspaper, the NSA can keep copies of intercepted communications from or about US citizens if the material contains significant intelligence or evidence of crimes.

The new details are the latest leaked by Snowden, who fled to Hong Kong and has been divulging previously secret programmes for collecting US phone records and internet data.

President Barack Obama and other top officials have defended the programmes, which again have raised the debate over national security and individual privacy.

Snowden went public in a video released by the Guardian on June 9 as the source of the leaked documents.

Private jet ready

Also on Thursday, an Icelandic businessman linked to the whistleblower site WikiLeaks said he has readied a private aircraft to take Snowden to Iceland if the government granted him asylum.

"We have made everything ready at our end now we only have to wait for confirmation from the [Icelandic] Interior Ministry," Olafur Vignir Sigurvinsson told Reuters news agency.

He is a director of DataCell, a company which processed payments for WikiLeaks.

"A private jet is in place in China and we could fly Snowden over tomorrow if we get positive reaction from the Interior Ministry," Sigurvinsson said. "We need to get confirmation of asylum and that he will not be extradited to the US.

"We would most want him to get a citizenship as well."

Earlier this week, Kristinn Hrafnsson, a WikiLeaks spokesman, said a middleman had approached him on behalf of Snowden to seek asylum in Iceland.

The Icelandic government, which has declined to say whether they would grant asylum to Snowden, confirmed it had received the message from Hrafnsson.

Source: Agencies