An airport mechanic may have planted the bomb on a Russian passenger plane which exploded over the Sinai Peninsula in October, killing all 224 people on board, according to sources connected with the case.
The Egypt government has denied that there is any evidence the MetroJet flight - which crashed shortly after takeoff from Sharm el-Sheikh airport on 31 October last year - was brought down by terrorism.
But anonymous sources told Reuters a man - whose cousin had left to join Isis 18 months ago - has been detained along with two airport policeman and another man allegedly suspected of helping him put the bomb on board.
The source said: "After learning that one of its members had a relative that worked at the airport, Islamic State (Isis) delivered a bomb in a handbag to that person.
"He was told to not ask any questions and get the bomb on the plane."
Another source said: "Two policemen are suspected of playing a role by turning a blind eye to the operation at a security checkpoint. But there is a possibility that they were just not doing their jobs properly."
Isis claimed responsibility for the attack on the aeroplane a few days after the crash - later explaining how they hid an improvised explosive device (IED) inside a soft drink can in their online propaganda magazine, Dabiq.
The crash has severely damaged Egypt’s tourist industry with the country reportedly losing £120m a month as the UK ban on flights to Sharm el-Sheikh continues.
The country’s security services came under fire following the attack after they were accused of lax enforcement of security protocols at their airports.
Tourists said they were offered the chance to skip baggage checks for a £20 bribe by men in military uniforms.
An Interior Ministry official said there had been no arrests and they were “awaiting results of the investigation”.
He said all potential airport staff and their families were screened and anyone who “shows sympathy to militants” was prevented from working at the airport.
A security official at the airline involved denied that any of their employees were under suspicion.
He said state security police had investigated all its workers at Sharm el-Sheikh airport and no evidence was found against them.
Additional reporting by Reuters
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