According to L’Express newspaper the order was made in a note from the PM's office, which was handed to ministries after the summer break.

In the letter dated August 19th, a senior member of Ayrault’s staff, Christopher Chantepy, listed a number of points ministers and their staff needed to take heed of in the future.

One of the demands that stood out was a request to ministers to stop using their smartphones for any sensitive communications, unless they were equipped with approved security devices.

The memo also told ministers to avoid sending text messages to each other.

To justify the measure, the circular pointed to the recent “security threats” in recent months, which is believed to be a reference to the American NSA's spying programme PRISM.

"The recent security breaches of information systems had led to us issuing a reminder of the basic rules," Ayrault's office said.

The NSA was alleged to have bugged diplomatic offices belonging to both France and the EU in New York and Washington.

Those allegations drew an angry response from Paris.

"We cannot accept this kind of behaviour between partners and allies," said the French president François Hollande, calling for it to “stop immediately”.

Even if the furore has died down somewhat in recent weeks, the French government is not taking any chances, it seems.

From now on any highly classified information must only be transmitted over specially encrypted telephones and all electronic documents can only be transferred using the government’s secure ISIS system, the French PM has ordered.

Although most documents will not be classified, the note from the PM warns: “they could harm individuals or the nation and efforts should be made to protect them.”

According to L’Express, which has published the note from the PM, the Interior Ministry has obeyed the instructions, with most members of staff using encrypted Samsung phones on which it is not possible to install applications and geo-tagging cannot be enabled.

However, several ministers and their staff are still opting to use their normal smartphones, l’Express reports.

In his note, the French PM has also warned staff not to insert a USB key unless they know exactly where it came from and that it is safe and not to click on any attachments in messages without checking them first.

Last month a French court opened a formal investigation into the PRISM program of electronic surveillance run by the US National Security Agency.