Documents leaked by US former spy Edward Snowden appear to show that Britain spied on foreign delegates including fellow NATO member Turkey at G20 meetings at the time, British newspaper The Guardian reported Monday.
"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" on the matter.
As with the other G20 participants who were reportedly spied on, including South Africa, there is no suggestion that Simsek and his party were involved in any kind of criminal offence, according to the newspaper.
The newspaper said it had seen a document showing 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".