WASHINGTON: The United States has launched a criminal investigation and is taking "all necessary steps" to prosecute Edward Snowden for exposing secret US surveillance programs, the FBI director said.
Robert Mueller, who is to step down soon after more than a decade leading the Federal Bureau of Investigation, defended the Internet and phone sweeps as vital tools that could have prevented the attacks of September 11, 2001.
Snowden's disclosures "have caused significant harm to our nation and to our safety", Mueller told lawmakers at a House Judiciary Committee hearing.
As to Snowden, "he is the subject of an ongoing criminal investigation," Mueller said. "We are taking all necessary steps to hold the person responsible for these disclosures."
Mueller's comments confirm that the US government is pursuing Snowden, the 29-year-old American IT specialist who has admitted to leaking information about far-reaching surveillance programs.
"The program is set up for a very limited purpose and a limited objective, and that is to identify individuals in the United States who are using a telephone for terrorist activities and to draw that network," he said.
Mueller told lawmakers that one of the 9/11 hijackers, Khalid al-Mihdhar, had called a known Al Qaeda safe house in Yemen from the US city of San Diego.
"If we had had this program in place at the time, we would have been able to identify that particular telephone number in San Diego," Mueller said.
Snowden, a technician working for a private contractor and assigned to an NSA base in Hawaii, surfaced over the weekend in Hong Kong to give media interviews.
In addition to disclosing the NSA's acquisition of phone logs and data from nine Internet giants — including Google, Microsoft and Facebook — Snowden also described secret global hacking operations.
On Friday, the South China Morning Post reported that Snowden has classified US documents showing the machines the NSA has targeted in China and Hong Kong.
IP addresses are unique numbers assigned to individual computers and other devices attached to the Internet. The SCMP did not publish the addresses or identify individuals who might have been targeted, or was able to confirm the authenticity of the information.
The documents however also showed whether a cyber attack was ongoing, and appeared to suggest a hacking success rate of 75 per cent.
"I don't know what specific information they were looking for on these machines, only that using technical exploits to gain unauthorised access to civilian machines is a violation of law. It's ethically dubious," Snowden told the newspaper.
US officials have also said the Internet monitoring program did not target Americans or even foreigners on US soil.
China has said little about the case, and foreign ministry spokeswoman Hua Chunying on Thursday dodged questions about whether Washington had sought Snowden's extradition and how China would react if he applied for asylum.