Leaks from ex-intelligence contractor Edward Snowden have damaged America's national security and he should return the secret documents he has "stolen," the US spy chief said Wednesday.
Snowden's disclosures since June have revealed the National Security Agency's vast electronic eavesdropping operations, sparking global outrage and prompting calls in Congress to curtail the NSA's powers.
But James Clapper, director of national intelligence, delivered a scathing condemnation of Snowden at a hearing of the Senate Intelligence Committee, saying his leaks have aided America's adversaries and undermined cooperation with foreign partners.
"What Snowden has stolen and exposed has gone way, way beyond his professed concerns with so-called domestic surveillance programs," Clapper said.
"As a result, we've lost critical foreign intelligence collection sources, including some shared with us by valued partners."
Clapper called on Snowden and his "accomplices" to return the classified documents that he took with him as the former NSA contractor has declared victory.
"Snowden claims that he's won and that his mission is accomplished," the intelligence chief said.
"If that is so, I call on him and his accomplices to facilitate the return of the remaining stolen documents that have not yet been exposed to prevent even more damage to US security."
Snowden, who has secured asylum in Russia and faces espionage charges from US authorities, has said he passed on the NSA classified files to journalists and no longer has them in his possession.
The former IT contractor has said in interviews that he feels vindicated as the leaks have prompted a global reaction and a political debate in the United States over the NSA's spying activities.
Clapper, however, said extremists and other US opponents "are going to school on US intelligence sources, methods and trade craft and the insights that they are gaining are making our job much, much harder."
US adversaries were changing the way they communicate as a result of the disclosures about NSA electronic spying and Snowden's leaks have jeopardized the lives of intelligence officers, diplomats and troops, according to Clapper.
The intelligence chief previously has acknowledged that the leaks have generated a useful debate about how to balance security with privacy rights.
The head of the Defense Intelligence Agency, Lieutenant General Michael Flynn, told the same hearing that Snowden's leaks have done "grave damage to our national security" and had put soldiers' lives at risk.
Snowden's disclosures included the revelation that the Americans tapped the mobile phone of German Chancellor Angela Merkel.
Earlier Wednesday, Merkel issued a strong rebuke to the United States and Britain over their extraordinary surveillance activities.
In a major speech to parliament ahead of talks with US Secretary of State John Kerry on Friday, Merkel said that Western powers sacrificing freedom in the quest for security were sending the wrong signal to "billions of people living in undemocratic states."