Turkey has reacted angrily to allegations that Britain spied on Finance Minister Mehmet Simsek's emails and phone calls when he was in London for the G20 summit.
The country's foreign ministry said on Monday that Turkey had contacted the UK for an explanation after documents leaked by US former spy Edward Snowden appeared to show Britain spied on G20 delegates during meetings back in 2009, Britain's Guardian newspaper has reported.
Among the officials targeted were delegates from NATO ally Turkey, and South Africa.
"It is clear that if the report is true, such an action by an ally country is unacceptable," the foreign ministry said in a statement, stressing that it was waiting for "an official and satisfying statement from British authorities".
"This will constitute a scandal in terms of relations between the two countries if any truth is found in the allegations," it said.
So far, British Prime Minister David Cameron has refused to comment on the issue.
The Guardian said the document showed that Britain's Government Communications Headquarters (GCHQ), its electronic eavesdropping agency, put Simsek under surveillance while in London, and possibly up to 15 members of his delegation as well.
The document stated that the objective was "to establish Turkey's position on agreements from the April London summit" and their "willingness (or not) to co-operate with the rest of the G20 nations".
Russia, meanwhile, has expressed concern that US spies may have intercepted communications made by the president Dmitry Medvedev, with politicians warning the allegations could harm ties between the two countries.
Britain used "ground-breaking intelligence capabilities" to monitor communications between officials at the two meetings in April and September of 2009, the paper reported on Monday.
The revelations are likely to be an embarrassment to Britain, which is hosting the two-day G8 summit in Northern Ireland from Monday.
|News that the US has been monitoring private data of people has been heavily criticised by civil rights groups
According to the files, British spies tricked delegates into using specially prepared Internet cafés. Those cafés allowed the spies to intercept communications and monitor email messages and phone calls through delegates' BlackBerry devices.
GCHQ was also able to track when delegates were contacting each other and the agency targeted certain officials, including the Turkish finance minister, according documents shown to the newspaper.
They also singled out South African computers for special attention, according to one document.
In a statement, South Africa said the country has "noted with concern various reports following a story published by the Guardian newspaper in the UK on allegations of spying on G20 country ministers and senior officials."
"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," the statement went on to say.
The Guardian also said that GCHQ received reports from a US National Security Agency attempt to listen in as then Russian president, Dmitry Medvedev, made a call via satellite to Moscow.
The documents suggest that orders to gather intelligence on delegates came from a senior level within the government of then prime minister, Labour's Gordon Brown, the Guardian said.
Two documents explicitly mention information being passed on to ministers.
Snowden is hiding in Hong Kong and the United States has launched a criminal investigation after the former CIA technical assistant blew the lid on the NSA's vast electronic surveillance operation.
The whistleblower says he has not revealed any US operations against legitimate military targets. Speaking in a Guardian online forum, he also said that the US government had "destroyed any possibility of a fair trial at home".
Leaders from the G8 nations meet in Lough Erne, Northern Ireland, on Monday for two days of talks on issues including the Syrian crisis, tax collection and free trade.