Flights were suspended on Sunday at Germany's Stuttgart airport over a false bomb alarm, local media reported.
German media Bild reported an argument between two passengers ended in one accusing the other of having planned an attack on the plane.
The remarks triggered immediate safety procedure by security staff.
The Bulgarian airliner, destined to Varna, was evacuated and thoroughly searched. Luggage was re-screened.
Other flights were also suspended due to the incident.
The threat turned out to be a false alarm, a spokesman for the federal police said.
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