The Delta Air Lines aircraft, flying from Paris to Kuwait, entered the Athens Flight Information Region(FIR) at 19.10 (2240 IST) Thursday, the same day the EgyptAir plane crashed in the Mediterranean shortly after leaving Greek airspace.
Its pilots failed to answer to repeated calls from the Greek Civil Aviation authorities, according to various media reports, confirmed to AFP by a Greek defence ministry source.
Following military protocol, at 19.49 two F-16 fighter jets intercepted the Delta airplane while it was flying near the Aegean island of Santorini.
The Ant1 Channel said that the pilots contacted Greek authorities at 19.55 and exited the Athens FIR at 20.10.
The incident occurred after the EgyptAir Airbus A320 carrying 66 people from Paris to Cairo disappeared off radar screens in the early hours of Thursday, without its crew sending a distress signal.
There was no suggestion of a link between the EgyptAir crash and the Delta incident.