Terrorists Planned Attack

The Federal Prosecutor's Office in Karlsruhe said in a statement that suspects had already convinced an airport employee with security access to smuggle a suitcase full of explosives onto a passenger plane.

Prosecutors have questioned six suspects about the bomb plot.

"With the exception of one suspect who is in prison for another offence, the other suspects were released on Saturday," the statement said.

Police also searched nine houses in the German states of Rhineland-Palatinate and Hesse over the weekend.

Suspected of belonging to terrorist organization

According to the prosecutor's office, the suspects had made contact several times with members of an unknown group without coming to an agreement on the size of the fee for smuggling the suitcase.

The prosecutor's office gave no details about the nationality of the suspects, nor would they reveal the planned timing of the attack.

In summer, Germany hosted the soccer World Cup, during which police were on high alert because of fears of terrorist attacks.

The German government on Monday said it would not increase its security warning in light of the new investigation.

"We always have to count on there being groups of people who are considering real plans," an interior ministry spokesperson said in Berlin.