Downing Street refused to comment on whether the Government had been given assurances by the United States that David Cameron's communications had not been monitored in the wake of allegations American spies had targeted German chancellor Angela Merkel's mobile phone.
The authorities in Berlin have summoned the US ambassador John B Emerson to meet foreign minister Guido Westerwelle, who will "spell out the position of the German government".
Mrs Merkel's government complained to president Barack Obama in a phone call yesterday after receiving information her phone may have been monitored.
The White House said it isn't monitoring and won't monitor Mrs Merkel's communications, but conspicuously didn't say whether they were monitored in the past.
But reports suggested that the US had denied ever spying on Mr Cameron.
Caitlin Hayden, a spokesman for the National Security Council told the Daily Telegraph: "We do not monitor PM Cameron's communications."
Asked if the US had ever spied on Mr Cameron in the past, she replied: "No."
At a regular briefing for journalists in Westminster the Prime Minister's official spokesman said: " I'm not going to comment on matters of security or intelligence."
Asked if he now worked on the assumption that his mobile phone was being tapped, Deputy Prime Minister Nick Clegg replied: "No".