A director of the government watchdog, the Federal Railways Office, told a parliamentary committee in Bonn of the series of events that caused the train to derail at 200 kph (125 mph), slamming into a bridge that then collapsed.

The worst train disaster in 50 years

Hans-Heinrich Grauf told the committee that the wheel broke due to an inner crack, about six kilometres from the site of the accident in the north of the country.

Mr Grauf said that after the broken wheel caused the train to derail, some of the carriages slipped under the overpass.

When one of the carriages slammed into the overpass, the bridge collapsed and the remaining carriages piled into each other.

Accident-free for seven years

Until the crash, the country's InterCity Express (ICE) trains had travelled the railway lines as a model of German technological prowess without an accident for seven years.

Since the accident the EBA watchdog has forced German railways to pull 59 ICE trains that were built in 1991 from service no less than three times for comprehensive testing.

"The railway has done everything in its power to ensure the safety of passengers," Deutsche Bahn railway chairman Johannes Ludewig told the committee.

The German transport minister, Matthias Wissmann, promised a full inquiry into the causes of the accident.

"Nothing will be swept under the carpet; nothing will be glossed over," he said.