German police released security camera footage on Friday

The man, 21, was detained at the main rail station in the city of Kiel.

The arrest follows the release of closed circuit TV footage of two male suspects by police on Friday.

The devices in abandoned suitcases on two trains failed to go off. Police said the bombers had intended to kill large numbers of people.

The student had been studying in the Baltic Sea port city of Kiel, where he was arrested in the early morning. He had been in Germany since 2004.

Chief prosecutor Monika Harms said he had apparently been planning to flee the country.

Reports say police searched his home in the city on Saturday afternoon.

He is believed to be "one of the two suspects that have been sought since yesterday with the help of video footage that was made public," the public prosecutors' office said.

In the video, the two suspects - dark-haired young men - are seen wheeling suitcases at Cologne station. Joerg Ziercke, head of Germany's Federal Crime Office, told reporters in the city he was confident that "we caught the right suspected bomb planter here in Kiel today".

Second suspect

Investigators first thought the bombs were part of a blackmail attempt, but they now believe the incident was the work of a terrorist group based in Germany.

Faulty construction may be why the devices failed to go off

A note written in Arabic, a telephone number in Lebanon, and packets of starch with labels in Arabic and English were found alongside the devices.

The authorities say they are investigating a possible link to Lebanon but they also haven't ruled out a link to Pakistan.

The identical suitcase bombs were fitted with timers set to go off 10 minutes before the trains arrived in Dortmund and Koblenz.

Police think they failed to detonate because of a construction flaw.

While the German authorities said the arrest is a major breakthrough in their investigation they warn that the second suspect is still at large.