David Cameron refused to answer questions on the GCHQ spying row as world leaders arrived for the G8 summit at Lough Erne in Northern Ireland.
The Guardian newspaper has said leaked documents show that in 2009 GCHQ organised surveillance of the country's delegation to an international summit in London.
Delegates had their computers monitored and phones intercepted on the orders of the British Government, it has been claimed.
The reports have the potential to embarrass the Prime Minister as he hosts leaders from the world's most powerful countries at the G8 summit in Northern Ireland - the biggest gathering of international statesmen to take place in the UK since the London G20.
The intelligence agencies were even said to have set up internet cafes specifically to enable them to read the emails of those taking part in the summit.
Asked whether he could guarantee his guests that no similar operation was in place at Lough Erne, David Cameron told Sky News: "We never comment on security or intelligence issues and I am not about to start now. I don't make comments on security or intelligence issues - that would be breaking something that no government has previously done."
According to The Guardian the Turkish finance minister - and possibly 15 other members of his party - were among those targeted in 2009.
The newspaper said the documents suggested that the 2009 operation was sanctioned at a senior level in the government of then prime minister Gordon Brown and that the intelligence obtained was passed to ministers.
Details of the eavesdropping were contained in documents obtained by Edward Snowden, the US National Security Agency (NSA) whistle-blower responsible for a string of disclosures about US intelligence operations.
The UK's Ambassador in Turkey has faced questions over the reports.
A Foreign Office spokesman confirmed that the Turkish government had raised the allegations with Sir David, but insisted he had not been summoned to answer questions in person.
A spokeswoman said: "I can confirm that the Turkish Ministry of Foreign Affairs raised the issue with the Ambassador.
"It was discussed in a phone call. He was not summoned."
During the course of the two summits in April and September 2009, GCHQ deployed what one document said were "ground-breaking intelligence capabilities" to monitor the communications of the visiting delegation.
They were said to have enabled a team of 45 analysts to be provided with live round-the-clock summaries of who was phoning whom during the proceeding.
The methods used included penetrating security of delegates' BlackBerrys in order to monitor their emails and phone calls.
Internet cafes were set up by GCHQ and MI6 able to "extract key logging info" for delegates, and provide the agencies with "sustained intelligence options against them" even after the summits were over.
There was what The Guardian described as a sustained campaign to penetrate the computers of the South Africans - which had access to their foreign ministry network.
British intelligence also received reports relating to an NSA attempt to listen in on the phone calls of then Russian leader Dmitri Medvedev as they passed through the satellite links to Moscow.
A briefing paper prepared for GCHQ director Sir Iain Lobban, dated January 9 2009, in preparation for a meeting with then foreign secretary David Miliband, set out the government's priorities for the G20 leaders' summit in April of that year.
"The GCHQ intent is to ensure that intelligence relevant to HMG's desired outcomes for its presidency of the G20 reaches customers at the right time and in a form which allows them to make full use of it," it noted.
A week after the September summit of finance ministers, an internal review concluded: "The call records activity pilot was very successful and was well received as a current indicator of delegate activity...
"It proved useful to note which nation delegation was active during the moments before, during and after the summit. All in all, a very successful weekend with the delegation telephony plot."
GCHQ previously said in relation to an earlier report about its involvement in NSA operations that its work was carried out "in accordance with a strict legal and policy framework which ensures that our activities are authorised, necessary and proportionate".