LONDON (AP) -- The Guardian newspaper said the British eavesdropping agency GCHQ repeatedly hacked into foreign diplomats' phones and emails when the U.K. hosted international conferences, even going so far as to set up a bugged Internet cafe in an effort to get an edge in high-stakes negotiations.
The news prompted an angry response from Russian officials concerned that their communications had been intercepted.
The report - the latest in a series of revelations which have ignited a worldwide debate over the scope of Western intelligence gathering - came just hours before Britain was due to open the G-8 summit in Northern Ireland on Monday, a meeting of the world's leading economies that include Russia. The allegation that the United Kingdom has previously used its position as host to spy on its allies and other attendees could make for awkward conversation as the delegates arrive for talks.
"The diplomatic fallout from this could be considerable," according to British academic Richard J. Aldrich, whose book "GCHQ" charts the agency's history.
Speaking at the G-8 summit, Prime Minister David Cameron declined to address the issue.
"We never comment on security or intelligence issues and I am not about to start now," he said. "I don't make comments on security or intelligence issues. That would be breaking something that no government has previously done."
GCHQ also declined to comment on the report.
Russian officials complained Monday about reports that their delegation had been snooped on in earlier summits.
"It's a scandal! The U.S. and British special services tapped (then President Dmitry) Medvedev's phone at the 2009 G-20 summit. The U.S. denies it, but we can't trust them," Alexei Pushkov, the Kremlin-connected chief of foreign affairs committee in the lower house of Russian parliament, wrote on his Twitter feed Monday.
Sergei Devyatov, a spokesman for the Federal Protection Service that provides security for top Russian government officials, said in a statement carried by the Interfax news agency: "The Federal Protective Service is taking every necessary measure to provide the appropriate level of confidentiality of information for top-ranking officials of the country."
The Guardian cites more than half a dozen internal government documents provided by former NSA contractor Edward Snowden as the basis for its reporting on GCHQ's intelligence operations, which it says involved, among other things, hacking into the South African foreign ministry's computer network and targeting the Turkish delegation at the 2009 G-20 summit in London.
Clayson Monyela, a spokesman for South Africa's foreign ministry, declined to comment on the report Monday when reached by telephone by AP. Monyela said on his Twitter feed that "the matter is receiving attention."
The source material - whose authenticity could not immediately be determined - appears to be a mixed bag. The Guardian describes one as "a PowerPoint slide," another as "a briefing paper" and others simply as "documents."
Some of the leaked material was posted to the Guardian's website with heavy redactions. A spokesman for the newspaper said the redactions were made at the newspaper's initiative, but declined to elaborate.
It wasn't completely clear how Snowden would have had access to the British intelligence documents, although in one article the Guardian mentions that source material was drawn from a top-secret internal network shared by GCHQ and the NSA. Aldrich said he wouldn't be surprised if the GCHQ material came from a shared network accessed by Snowden, explaining that the NSA and GCHQ collaborated so closely that in some areas the two agencies effectively operated as one.
One document cited by the Guardian - but not posted to its website - appeared to boast of GCHQ's tapping into smartphones. The Guardian quoted the document as saying that "capabilities against BlackBerry provided advance copies of G-20 briefings to ministers." It went on to say that "Diplomatic targets from all nations have an MO (a habit) of using smartphones," adding that spies "exploited this use at the G-20 meetings last year."
Another document cited - but also not posted - concerned GCHQ's use of a customized Internet cafe which was "able to extract key logging info, providing creds (credentials) for delegates, meaning we have sustained intelligence options against them even after conference has finished." No further details were given, but the reference to key logging suggested that computers at the cafe would have been pre-installed with malicious software designed to spy on key strokes, steal passwords and eavesdrop on emails.
Aldrich said that revelation stuck out as particularly ingenious.
"It's a bit `Mission Impossible,'" he said.