"These explosions were meant to go off," Joerg Ziercke, the head of the Federal Criminal police, said at a press conference in Germany today.
If successful, the attack would have been the third such attack on an European mass transit system, following bombs placed on Madrid and London trains and subways.
German officials said two suitcase bombs, containing bottles of gas, had been placed on trains in Koblenz and Dortmund. The officials said there were strong indications of an organized terror attack.
"We have found pieces of paper with Arabic letters and telephone numbers from Leganon in the clothes which were in the suitcases to insulate or fix the gas bottles," Ziercke said.
Police released photos taken by surveillance cameras in German train stations of suspects carrying large backpacks.
Police said it was not clear why the bombs failed to detonate, but that they had been wired to go off at the same time.