THE Attorney General of the United States has warned the whistleblower who leaked details on the country's internet spying tactics that he will be caught.
Eric Holder reiterated claims that defence contractor turned fugitive Edward Snowden had damaged US national security and the safety of Americans and their allies.
"I can assure you that we will hold accountable the person who is responsible for these extremely damaging leaks," Mr Holder said.
"The national security of the United States has been damaged as a result of these leaks. The safety of the American people, the safety of the people who reside in allied nations have been put at risk as a result of these leaks.
"We are presently in the process of this investigation and I am confident that the person who is responsible will be held accountable."
Mr Holder, in Dublin for talks with European Union home affairs and justice ministers and officials, made the declaration as Mr Snowden remains on the run.
He disappeared from a luxury Hong Kong hotel this week after giving his first interviews on the online surveillance.
Mr Snowden, 29, a former technical assistant at the CIA, revealed himself as the source of top-secret documents about the National Security Agency's (NSA) monitoring of phone and internet data after he walked away from his job in Hawaii with security contractor Booz Allen Hamilton.
The US AG was facing calls from Ireland's Justice Minister, Alan Shatter, for greater transparency on when data was being accessed.
Mr Holder assured European officials that spies could only snoop on foreign individuals and organisations with a court order and oversight from Congress.
He said surveillance will only be allowed where there is documented evidence to support suspicions that an individual has links to "terrorism, hostile cyber activities or nuclear proliferation".
Mr Holder insisted "appropriate or documented foreign intelligence" is required to give spies the green light.
Mr Holder said internet service providers supply the US government with information on individuals only when they are lawfully required to under the Prism programme.
"The Government cannot target anyone under the court-approved procedures for this programme unless there is an appropriate and a documented foreign intelligence purpose for the acquisition," he said.
"That is, such as for the provision of terrorism, hostile cyber activities or nuclear proliferation, and the foreign target is reasonably believed to be outside the US.
"We cannot target every foreign person overseas without a valid foreign intelligence purpose."
The AG said all activities involved with the programme are subject to "an extensive oversight regime", involving the US executive, legislature, judicial bodies, Congress and the courts.
He said intelligence services could not arbitrarily access communications data, following reported links between UK eavesdropping agency GCHQ and the US's controversial Prism internet monitoring programme.