The US House of Representatives narrowly approved continuing the National Security Agency's secret collection of hundreds of millions of citizens' phone records after a fierce debate pitting privacy rights against the government's efforts to thwart terrorism.

Wednesday night's 217-205 vote was unlikely to be the final word on government intrusion to defend the United States and its nationals' civil liberties.

The vote marked the first chance for lawmakers to take a stand on the secret surveillance program since former National Security Agency systems analyst Edward Snowden leaked classified documents last month that spelled out the monumental scope of the government's activities.

Snowden awaits go-ahead to leave Moscow airport Fugitive US intelligence leaker Edward Snowden on Thursday awaited permission to leave the Moscow airport where he has been stuck for over a month as the United States stepped up pressure on Russia to send him back home. Reports on Wednesday indicated that Russian authorities were preparing to let Snowden leave the transit zone of Sheremetyevo Airport but then - in mysterious circumstances - he failed to emerge. Snowden has applied for asylum in Russia and is now awaiting a document that would allow him to formally cross the border and move freely in Russia while his application is being considered - a prospect the United States has said would be "deeply disappointing". Russian Foreign Minister Sergei Lavrov spoke with US Secretary of State John Kerry about Snowden's case on Wednesday, but it was not clear if their discussion had an impact on the fugitive's fate. The US ambassador in Russia on Thursday reiterated that Washington wants Moscow to hand over Snowden, despite the absence of an extradition agreement between the two countries. "The US is not asking for 'extradition', but simply the return of Mr Snowden. We have sent many people back to Russia," Ambassador Michael McFaul said on Thursday morning. - AFP

Republican Representative Justin Amash had challenged the program as an indiscriminate collection of phone records, saying his effort was to defend the US Constitution and "defend the privacy of every US citizen". On Twitter, he vowed: "We fight on".

His measure, offered as an addition to a $598.3 billion defense-spending bill for 2014, would have canceled the statutory authority for the NSA program, ending the agency's ability to collect phone records and metadata under the USA Patriot Act unless it identified an individual under investigation.

The House later voted to pass the overall defense bill, 315-109.

The issue created unusual political coalitions in Washington, with the Barack Obama administration, national security leaders in Congress and the Republican establishment facing off against libertarian-leaning conservatives and some liberal Democrats.

The measure challenging the surveillance program faces strong opposition in the Senate and from the White House and is unlikely to survive in a final spending bill.

"Have 12 years gone by and our memories faded so badly that we forgot what happened on Sept 11?" Representative Mike Rogers, the Republican chairman of the intelligence committee, said in pleading with his colleagues to back the program.

With a flurry of letters, statements and tweets, both sides lobbied furiously in the hours prior to the vote in the Republican-controlled House. The director of national intelligence, James Clapper, warned against dismantling a critical intelligence tool.

Since the Sept 11, 2001, attacks, US Congress has authorized - and a Republican and a Democratic president have signed - an extension of the powers to search records and conduct roving wiretaps in pursuit of terrorists.

Since the disclosures this year, however, lawmakers have said they were shocked by the scope of the two programs - one to collect records of hundreds of millions of calls and the other allowing the NSA to sweep up Internet usage data from around the world that goes through nine major US-based providers.

An earlier report from Foreign Policy magazine revealed the CIA's off-net operation in the digital age, known as the "black bag job", in which CIA operators were trained to physically bug, tap or steal information when the NSA cannot gain access to certain computers.

According to the magazine, sources within the US intelligence community confirmed that, since Sept 11, 2001, the operations have given the NSA access to a number of new and critically important targets around the world, especially in China and elsewhere in East Asia, as well as the Middle East and South Asia.

Ministry of National Defense spokesman Geng Yansheng said on Thursday that Beijing has noticed such reports. "A series of incidents recently reminded us that we should pay more attention to protecting the Internet and information security and firmly safeguard national cybersecurity."

China Daily contributed to this story.