German authorities are investigating a group of people in connection with what they suspect was a foiled plot to smuggle a bomb onto a passenger plane, prosecutors said on Monday.
German security sources said on condition of anonymity the plane would have been at Frankfurt International Airport, one of the world's busiest. One source confirmed German media reports that the target was a plane belonging to Israel's El Al airline.
An El Al spokeswoman in Israel said the company does not respond to reports about security matters.
Federal prosecutors in Karlsruhe said they were investigating six suspects whom they had identified and a number of unidentified suspects.
None of the names or details of the suspects have been made public, although a security source told Reuters the suspects were from Jordan, Kuwait and Iraq. Der Tagesspiegel newspaper reported that most were Jordanians of Palestinian origin.
Several of the suspects had approached someone during the summer who had access to the security department at a German airport and who had expressed willingness to smuggle a suitcase or bag onto a plane for payment, a statement said.
The suspects repeatedly made contact with the person but were unable to agree on a price for planting a bomb, it said. Die Welt said the person was a male employee of Frankfurt airport.
"The suspects were temporarily taken into custody and informed of the suspicions against them before they were released on Saturday, with the exception of one wanted in connection with another crime," the office said.
The men are suspected of being members of a terrorist organization, the office said. It did not explain why the suspects, who remain under investigation, had been released.
"I can't comment on the particularities about the decision to release them," said a spokesman for the Interior Ministry. Germany's BND foreign intelligence agency also declined comment.
The prosecutor's office said it had searched nine apartments on Friday in the western German states of Rhineland-Palatinate and Hesse to gather evidence.
Four Arab men were convicted in a German court last year of plotting to bomb Jewish targets in Berlin and Duesseldorf in 2002 under orders from the late leader of al Qaeda in Iraq Abu Musab al-Zarqawi, who was killed by the U.S. Military in June.
Police uncovered a failed plot by two young Lebanese men to detonate suitcase bombs on trains in western Germany in July.
A Hamburg-based al-Qaeda cell has been blamed for the Sept. 11, 2001, hijacked-plane attacks on the United States. Since then, Germany has cracked down on Muslim militants and has put on trial a number of radical Islamists.