The remains of a Russian airliner which crashed is seen in central Sinai near El Arish city, north Egypt on 31 October Reuters

An Egypt Air mechanic, who is the cousin of an Isis fighter, has been detained on suspicion of being the mole at an Egyptian airport who planted an explosive device on a Russian plane that blew up in mid-air late last year, it has been reported. Security sources told Reuters that the aircraft worker is the main suspect in the crash of Metrojet flight KGL9268 that came down in the restive Sinai Peninusla last October.

All 217 passengers and seven crew member were killed in the incident, which Russia and the West have long maintained was caused by a detonation on board. Egypt has however never confirmed the circumstances, despite a claim of responsibility by the Islamic State (Isis) group.

Security officials, speaking on condition of anonymity have now told the news agency that investigators believe a worker with Egypt's flag-carrier airline was indeed responsible for putting a bomb on to the aircraft, as it was waiting to take off from Sharm el-Sheikh's airport.

"After learning that one of its members had a relative who worked at the airport, Islamic State delivered a bomb in a handbag to that person," said one of the sources. A baggage handler and two airport policemen suspected of helping the operation have also reportedly been arrested.

Egypt Air and the Interior Ministry have, however, denied any arrest has been made, saying the investigation was still ongoing. The Airbus A321 was 23 minutes into its flight to St Petersburg when it disappeared from radar screens on 31 October 2015.

Experts from France's bureau of enquiry and analysis for aviation security (BEA) assisting the Egyptian probe earlier said flight data recordings suggest it had suffered a sudden and abrupt demise consistent with a bombing.

In the weeks after the incident, which raised concerns over the level of security checks at Egyptian airports and delivered a blow to the country's tourism industry, a number of flights were suspended over security concerns. Britain was first to halt all flights in and out Sharm el-Sheikh, while, days later, Russia banned all Egypt Air flights from landing in its territory.