Edward Snowden took up a position at a US government defence contractor specifically to gather evidence on Washington's surveillance programmes, he told the South China Morning Post in remarks published Tuesday.

He joined Booz Allen Hamilton to collect proof about the US National Security Agency's secret programmes with the aim of releasing the details to the media, he said in the interview on June 12.

The publication of the admission comes after Snowden left Hong Kong for Moscow, with US officials angrily demanding that Russia hand him over for trial, and slamming China for letting him go.

"My position with Booz Allen Hamilton granted me access to lists of machines all over the world the NSA hacked," he told the Post. "That is why I accepted that position about three months ago."

The newspaper said when he was asked if he specifically went to Booz Allen Hamilton to gather evidence of surveillance, he replied: "Correct on Booz."

The company sacked Snowden after he leaked the details of the US Internet and phone data surveillance programmes to the press, saying he had violated the company's code of ethics.

Snowden was employed by Booz Allen Hamilton to help maintain the NSA's secret computer networks in Hawaii, and left with what he says was large quantity of classified documents related to its surveillance programmes.

The 30-year-old technician fled Hawaii on May 20 and flew to Hong Kong, a semi-autonomous Chinese territory, from where he proceeded to leak details of secret US intelligence programmes to international media outlets.

He has asked Ecuador for asylum.