An investigation has been launched after Arabic graffiti was found daubed on panels covering the fuel tanks of four easyJet planes at French airports. The airports cannot be identified for security reasons.

Lisa King, easyJet cabin safety manager, alerted company employees to the graffiti with an email, informing them of the discovery of "four aircraft in France with written inscriptions on the inside of the fuel panel, and toilet door in Arabic script".

According to The Telegraph, the airline did not give any details of the nature of the inscriptions. A spokeswoman for easyJet said the incident was not considered to be a security threat, either by the airline or the authorities, and no passengers had to be removed from the aircraft.

She said: "EasyJet assessed this issue, each time working in full consultation with the authorities, and is entirely satisfied it is nothing more than graffiti. EasyJet takes very seriously any security related issue and would not operate a flight unless we are entirely satisfied it is completely safe to do so. EasyJet operates its fleet of aircraft in full compliance with all regulations. The safety and security of its passengers and crews is always easyJet's highest priority."

Philip Baum, editor of Aviation Security International, told The Sun: "Graffiti in itself won't hurt anybody. But the ability of anyone to place a prohibited item near fuel tanks is a concern, of course. We know there are people working in restricted areas of airports with extremist sympathies."

An investigation is underway to determine who made the inscriptions. The graffiti was found two weeks after 130 people were killed in terror attacks in Paris.

On November 20, an easyJet flight was evacuated at Manchester airport following a bomb hoax, after a passenger claimed to have explosives in his bag. Passengers were asked to disembark after the plane's captain alerted police to the potential threat.