Dusseldorf - Four men on trial in Germany for a terrorist bomb plot have started making extensive confessions, their defence lawyer said on Thursday.

Federal Criminal Police officers had begun hearings on Tuesday, in the prisons where the men were being held, said defence lawyer Axel Nagler, adding that "the statements are very extensive."

German police arrested the plotters in September 2007 after they bought chemicals, allegedly to blow up US bases on behalf of the Islamic Jihad Union (IJU), a shadowy group said to be as dangerous as al-Qaeda.

All four defendants had initially refused to talk to police or to answer questions by the presiding judge in the Dusseldorf court.

Key allegations against the four men are backed by evidence, gathered through months of extensive police surveillance.

The police used listening devices to follow the plot and kept detailed notes of their entire surveillance of Fritz Gelowicz, Daniel Schneider and Adem Yilmaz. The first two are ethnic Germans who converted to Islam while Yilmaz is of Turkish descent.

The group bought 730 kilograms of hydrogen peroxide, a bomb-making chemical, and detonators, but had not fixed a target when they were arrested, though they allegedly outlined plans for three car bombs and an attack on an airbase without using a car.

The trial, one of Germany's biggest ever terrorism cases, is being adjourned while the hearings take place, and is due to resume next week. (dpa)