German prosecutors said on Monday they had uncovered a terrorist plot to blow up a passenger plane in Germany using explosives hidden in luggage.
"During the summer, several suspects made contact with an individual who had access to the security-restricted zone of an airport," said a statement from the federal prosecutor's office.
The individual agreed to smuggle explosives concealed in a case or a bag onto a plane in return for payment, it added.
But the plan fell apart when the as-yet-unidentified suspects failed to reach agreement with the airport employee on the payment he was to receive.
A report in Die Welt newspaper to be published on Tuesday said the intended target was a plane operated by the Israeli airline El Al from Frankfurt airport.
Die Welt quoted the security services as its source, but the prosecutor's office gave no details of which plane or airport was to have been involved.
Six suspects were arrested in Germany on Friday in connection with the alleged plot, but five were released the following day. A sixth person was kept in custody in connection with a different offence.
All six suspects are being investigated for allegedly belonging to a terrorist organisation. Their suspected accomplices, who have yet to be identified, are also being sought.
Investigators searched nine apartments in the southern region of Rhineland-Palatinate and Hesse in central Germany looking for evidence, a spokesman said.
An interior ministry spokesman said the alleged plot showed that Germany was in the terrorists' sights.
Germany was shaken in the summer after it was discovered that home-made bombs hidden in suitcases failed to explode on two passenger trains in an apparent bid to copy the devastating train bombings in Madrid and London.
Two Lebanese men have been charged with planting the devices on trains heading for the western cities of Hamm, near Dortmund, and Koblenz, on July 31.
Germany's federal prosecutor Monika Harms warned last week that although no attack had taken place on German soil recently, the apparent peace "could be deceptive" and the country must remain vigilant.
British authorities have charged 11 people with conspiracy to murder and preparing an act of terrorism after police foiled an alleged plot to blow up passenger jets bound for the United States in August.