Jörg Ziercke, president of the BKA Federal Police Office told the Bild am Sonntag newspaper that at the current time, "there are no indications of further terrorist cells," although he did not rule out further arrests in connection with train bombing case.

Ziercke did say he was "very concerned" that the terrorist danger in this instance was recognized so late, only after the suitcase bombs placed on two commuter trains in western Germany failed to explode.

On Saturday, authorities issued an arrest warrant for a Syrian man alleged to have been involved in the plot. The 23-year-old student, identified as Fadi A.S., was believed to have done research on the Internet with other suspects on how to construct a bomb like the ones found in the suitcases left on the trains.

Regarding a possible connection between the suspects and the al Qaeda terrorist network, Ziercke said only that that question is one that still has to be answered.

"The war on terror has been very difficult for al Qaeda and it no longer has the operational abilities is did around the time of Sept. 11," he said. "However, al Qaeda is trying to create new cells."

Imams under new scrutiny

According to federal police president, 99.9 percent of Muslims living in Germany are peace loving, adding that they had a responsibility, if they see young people turning radical, to report them to security authorities.

He announced that so-called "hate preachers" in mosques would be dealt with more severely than they have been in the past.

"I wonder why anyone is allowed to preach in German mosques," he said. "Shouldn't imams be trained and reviewed here in Germany?"

New kind of terrorism for Germany

Germany's federal prosecutor, Monika Harms, told German public television on Sunday she hoped investigators' efforts met with further success.

"I don't rule out the possibility that there are more people involved," she said, adding that investigators had "numerous leads" due to the computer belonging to Fadi A.S. that was confiscated in Constance.

She was also cautious about making a firm connection between al Qaeda and the young men suspected of being behind the attacks. According to her, they belonged to a small group without a fixed structure that had decided to take action spontaneously.

"That is different, but not less dangerous" as the terrorism that shook Germany in the 1970s, she said.