Media playback is unsupported on your device Media caption "We've lost critical foreign intelligence collection sources, including some shared with us by valued partners," Clapper said

The US spy chief has demanded intelligence leaker Edward Snowden return the documents he has "stolen".

At a US Senate hearing, Director of National Intelligence James Clapper harshly condemned the fugitive ex-intelligence contractor, saying his leaks caused "profound damage".

Mr Clapper said the leaks had gone "way beyond [Mr Snowden's] professed concerns" about domestic spying.

Mr Snowden remains in Russia on asylum but faces espionage charges in the US.

The documents from the National Security Agency (NSA) that Mr Snowden has leaked to journalists have shed new light on electronic spying operations in the US and UK.

Among other revelations, the documents showed the NSA collected data on millions of phone calls, collected millions of text messages per day, tapped the mobile phone of German Chancellor Angela Merkel, sought to collect intelligence by spying on users' mobile apps, and more.

Some of the intelligence was shared with British spies in the Government Communications Headquarters (GCHQ), according to the documents.

Mr Snowden, who was a contract computer technician for the NSA before he fled the US last year, has said he no longer has copies of the documents.

'Accomplices'

"Snowden claims that he's won and that his mission is accomplished," Mr Clapper told the Senate intelligence committee on Wednesday.

"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."

Mr Clapper did not clarify whom he meant by "accomplices", but his spokesman told the Associated Press news agency he "was referring to anyone who is assisting Edward Snowden to further threaten our national security through the unauthorised disclosure of stolen documents related to lawful foreign intelligence collection programs".

The former NSA contractor has said in recent interviews he believes the leaks have prompted a global reaction and a political debate within the US over spying programmes.

Image copyright AP Image caption Protesters with anti-war group Code Pink heckled Clapper at the Senate intelligence committee briefing

But Mr Clapper said on Wednesday the leaks had damaged US national security and undermined co-operation with the country's foreign partners.

US enemies "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," he said.

Ahead of talks with US Secretary of State John Kerry on Wednesday, Ms Merkel said in a speech that US and UK spying "sows distrust" among allies and sent the wrong signal to "billions of people living in undemocratic states".

As the hearing opened on Wednesday, protesters heckled Mr Clapper - one saying: "Should we be asking for James Clapper's resignation for lying to Congress?"

The intelligence chief has been criticised for telling legislators during a hearing last year the US did not collect data on millions of Americans, though Mr Snowden's leak has suggested the NSA had indeed been gathering data on calls of many Americans.