German investigators said on Friday they suspected that homemade bombs found on two trains last month were a failed terror attack.
It was first thought that the devices packed into cases in trains in the western cities of Dortmund and Koblenz on July 31 were a blackmail attempt, but analysis of the contents has revealed a possible link to Lebanon.
"We are now working on the basis that this was the work of a terrorist group based in Germany and that it was an attempt to kill a large number of people," Rainer Griesbaum, a federal prosecutor, said at a press conference.
The head of the Federal Crime Office, Joerg Ziercke, said the devices were packed into identical black cases and consisted of gas canisters, alarm clocks, wires and batteries and soft drink bottles filled with a flammable liquid.
"The cases had been supposed to explode 10 minutes before the trains arrived at the stations," Ziercke said.
He said a team of 100 investigators were still trying to find out why the devices failed to explode. "We still have many unanswered questions," he said.
A note in one of the cases contained Arabic writing and a telephone number in Lebanon and packets of starch with labels in Arabic and English were also found.
The cases containing the bombs were unaccompanied when they were discovered in the trains, but closed circuit television cameras recorded pictures of two dark-haired young men, one wearing a Germany football shirt, wheeling the cases on to platforms at the Cologne station.
Investigators have offered a reward of 50,000 euros (64,000 dollars) for information leading to the arrest of the men.