It was recently revealed the United Kingdom's secret wiretapping agency GCHQ monitored the communications of the politicians and senior officials from Turkey, South Africa and Russia during the G20 summit, The Guardian reported.
"The allegations in the Guardian are very worrying. ... If these allegations are true, this is going to be scandalous for the U.K. At a time when international co-operation depends on mutual trust, respect and transparency, such behavior by an allied country is unacceptable," a statement from Turkey's foreign ministry said.
South African officials also expressed concern over the alleged surveillance.
"We do not yet have the full benefit of details reported on but in principle we would condemn the abuse of privacy and basic human rights particularly if it emanates from those who claim to be democrats," a statement from the South African foreign ministry said.
The statement added: "We have solid, strong and cordial relations with the United Kingdom and would call on their government to investigate this matter fully with a view to take strong and visible action against any perpetrators."
Meanwhile, a former head of Russia's security services said Monday spying on then-Russian President Dmitry Medvedev during the summit would have been relatively easy but not a good idea, RIA Novosti reported.
"From a technical point of view, monitoring the conversations of people in your own country is not at all complicated," said Nikolai Kovalyov, a member of Russia's State Duma's Security Committee and a former head of the Federal Security Service. "It's another matter that intelligence services are forbidden from doing such things to avoid a diplomatic and international scandal, and they usually don't do them."
The alleged spying took place during a world leaders' summit meeting April 2, 2009, and at a finance ministers meeting the following September shortly before a Sept. 25 Pittsburgh G20 meeting hosted by President Barack Obama, The Guardian reported.
The newspaper based its report on a review of top-secret documents stolen by U.S. rogue ex-contractor Edward Snowden.
The April heads of state and government meeting was hosted by Gordon Brown, Britain's prime minister at the time.
The alleged spying was approved at a senior level of Brown's Labor Party government, The Guardian said.
The London and Pittsburgh summits focused on the fast-growing global financial crisis and came five months after a Washington G20 world leaders summit on the crisis, also hosted by Obama, Nov. 14-15, 2008.
The documents The Guardian cited indicated during the two London meetings, Britain's Government Communications Headquarters intelligence agency used what one document called "groundbreaking intelligence capabilities" to intercept visiting delegations' communications.
GCHQ is the counterpart of the U.S. National Security Agency, whose cellphone and Internet data sweeps were leaked by Snowden to The Guardian and The Washington Post, and published starting 11 days ago.
The latest surveillance, The Guardian reported, included British surveillance agencies:
-- Setting up Internet cafes where agents from GCHQ, the Secret Intelligence Service, commonly known as MI6, and others used email-interception and password-logging software to spy on delegates' computer use.
-- Penetrating delegates' BlackBerry smartphone security to monitor their emails and phone calls.
-- Giving live, round-the-clock summaries of who at the summit was phoning who to 45 intelligence analysts.
-- Targeting Turkish Finance Minister Mehmet Simsek, who has both British and Turkish citizenship, and possibly 15 others in Turkey's ruling Justice and Development Party. The party is currently the subject of anti-government protests in Istanbul and other parts of Turkey.
-- Receiving reports from an NSA attempt to eavesdrop on Dmitry Medvedev, Russia's president then, as his phone calls passed through Moscow satellite links. Vladimir Putin, Russia's current president, is at the Group of Eight summit in Northern Ireland beginning Monday. That meeting is hosted by British Prime Minister David Cameron.
The April intelligence information was intended to make sure Brown's "desired outcomes" of the leaders summit reached British ministers and other "customers at the right time and in a form which allows them to make full use of it," a document cited by the newspaper said.
The September spying on G20 finance ministers included an objective "to establish Turkey's position on agreements from the April London summit" and its "willingness [or not] to cooperate with the rest of the G20 nations," a document cited by the newspaper said.
During that meeting, intelligence agencies used a new surveillance technique to provide live reports of all delegate phone calls and to display all calls on a graphic that was projected onto a 50-square-foot video wall at GCHQ's operations center. The Guardian said. The information was also sent to the computers of 45 specialist analysts monitoring the delegates, the newspaper said.
"For the first time, analysts had a live picture of who was talking to who that updated constantly and automatically," an internal review quoted by the newspaper said.
One of the results of the London and Pittsburgh summits was that the countries agreed the G20 would become the new permanent council for international economic cooperation, replacing the G8, which would focus on security issues.