(CNN) -- Britain's electronic intelligence agency monitored delegates' phones and tried to capture their passwords during an economic summit held there in 2009, the Guardian newspaper reported Sunday.
The targets included British allies such as Turkey and South Africa, the newspaper reported. The Guardian cited documents provided by Edward Snowden, the American computer analyst now spilling secrets of the U.S. intelligence community.
The latest report was published on the eve of another economic summit hosted by the British government -- the Group of Eight economic summit in Northern Ireland. According to the newspaper, the documents show that the British signals intelligence agency GCHQ used "ground-breaking intelligence capabilities" to intercept calls made by members of the larger G-20 conference delegations at meetings in London.
Analysts received round-the-clock summaries of calls that were being made, and GCHQ set up Internet cafes for delegates in hopes of intercepting e-mails and capturing keystrokes, the Guardian reported. One briefing slide explained that would give intelligence agencies the ability to read delegates' e-mails "before/as they do," providing "sustained intelligence options against them even after conference has finished."
GCHQ is Britain's equivalent of the National Security Agency, the highly secretive U.S. communications intelligence service. The Guardian reported that the NSA had attempted to eavesdrop on then-Russian President Dmitry Medvedev during the conference as his phone calls passed through satellite links to Moscow and briefed its British counterparts on the effects.
Snowden, 29, worked for the NSA through a private contractor firm until May, when he decamped to Hong Kong. He went public a week ago as the source of articles by the Guardian and The Washington Post, saying the NSA's efforts posed "an existential threat to democracy."
Shawn Turner, a spokesman for the Office of the Director of National Intelligence, said Sunday he was aware of the Guardian's latest report but declined to comment on it.
"What we should be focused on is how irresponsible and egregious these recent leaks are," he told CNN. "It's impossible to know exactly how much damage is being done by these disclosures, but they will have an effect on our counterterrorism efforts."
Snowden's revelations about the NSA's collection of millions of records from U.S. telecommunications and technology firms have led to a furious debate within the United States about the scale and scope of surveillance programs that date to the days after the 2001 al Qaeda attacks on New York and Washington. Defenders say the programs -- approved by Congress after a warrantless surveillance effort under the Bush administration was revealed in 2005 -- have protected American lives by helping agents break up terrorism plots.
Retired Gen. Michael Hayden, a former NSA director, told CNN's Fareed Zakaria GPS that what the agency collects are "essentially billing records" that detail the time, duration and number of a phone call. The records are added to a database that agents can query in cases involving a terror investigation overseas, and agents can't eavesdrop on Americans' calls without an order from a secret court that handles intelligence matters, he said.
If a phone number related to that investigation has links to a domestic phone number, "We've got to go back to the court," he said.
But critics such as Sen. Mark Udall, a member of the Senate Intelligence Committee, had raised questions about the scale of the program even before Snowden's leak. Udall told NBC's "Meet the Press" on Sunday that he doesn't believe the program is making Americans any safer, "and I think it's ultimately, perhaps, a violation of the Fourth Amendment."
"I think we owe it to the American people to have a fulsome debate in the open about the extent of these programs," said Udall, D-Colorado. "You have a law that's been interpreted secretly by a secret court that then issues secret orders to generate a secret program. I just don't think this is an American approach to a world in which we have great threats."
But President Barack Obama does not feel that he has violated the privacy of any American, his chief of staff, Denis McDonough, told CBS' "Face the Nation." McDonough said the president will discuss the need to "find the right balance, especially in this new situation where we find ourselves with all of us reliant on Internet, on e-mail, on texting."
Shortly after the stories broke, Obama publicly defended the NSA programs as "modest encroachments on privacy" that help prevent terrorism.
CNN's Jessica Yellin contributed to this report.