The French government has summoned the US ambassador in Paris, demanding an explanation about claims that the National Security Agency has been engaged in widespread phone surveillance of French citizens.

On Monday, Le Monde published details from the NSA whistleblower Edward Snowden suggesting that the US agency had been intercepting phone calls on what it termed "a massive scale".

The French foreign minister, Laurent Fabius, warned: "This sort of practice between partners that invades privacy is totally unacceptable and we have to make sure, very quickly, that this no longer happens."

His summoning of the ambassador for urgent talks came as the US secretary of state, John Kerry, arrived in the French capital for the start of a European tour focused on discussions on the Middle East, especially Syria, and keen to stress Washington's close military and intelligence ties with Paris, which he recently called the "oldest ally" of the US.