The British government spied on politicians and officials who participated in two G20 summit meetings in London in 2009, the Guardian reports.
UK intelligence agencies monitored the G20 participants' computers and intercepted their phone calls, according to documents provided by NSA whistleblower Edward Snowden and seen by the Guardian.
Some delegates were tricked into using internet cafes which had been set up by British intelligence agencies to read their email traffic, the Guardian adds.
More from the Guardian:
The revelation comes as Britain prepares to host another summit on Monday – for the G8 nations, all of whom attended the 2009 meetings which were the object of the systematic spying. It is likely to lead to some tension among visiting delegates who will want the prime minister to explain whether they were targets in 2009 and whether the exercise is to be repeated this week.
The disclosure raises new questions about the boundaries of surveillance by GCHQ and its American sister organisation, the National Security Agency, whose access to phone records and internet data has been defended as necessary in the fight against terrorism and serious crime. The G20 spying appears to have been organised for the more mundane purpose of securing an advantage in meetings. Named targets include long-standing allies such as South Africa and Turkey.
There have often been rumours of this kind of espionage at international conferences, but it is highly unusual for hard evidence to confirm it and spell out the detail. The evidence is contained in documents – classified as top secret – which were uncovered by the NSA whistleblower Edward Snowden and seen by the Guardian. They reveal that during G20 meetings in April and September 2009 GCHQ used what one document calls "ground-breaking intelligence capabilities" to intercept the communications of visiting delegations.
• Setting up internet cafes where they used an email interception programme and key-logging software to spy on delegates' use of computers;
• Penetrating the security on delegates' BlackBerrys to monitor their email messages and phone calls;
• Supplying 45 analysts with a live round-the-clock summary of who was phoning who at the summit;
• Targeting the Turkish finance minister and possibly 15 others in his party;
• Receiving reports from an NSA attempt to eavesdrop on the Russian leader, Dmitry Medvedev, as his phone calls passed through satellite links to Moscow.