German prosecutors have charged four men with membership of a terrorist organisation.
The men are accused of planning to carry out an al-Qaeda attack using homemade bombs.
The group's leader, 30-year old Moroccan Abdeladim el-Kebir, is also charged with training at a terrorist camp on the Afghan-Pakistan border.
Prosecutors say he recruited the group's other members, whose full names have not been given.
The other men charged are German-Moroccan Jamil S, who is accused of producing explosives, German-Iranian Amid C and German Halil S, 27, who are alleged to have carried out mostly logistical tasks.
According to German officials, a senior al-Qaeda figure on the Afghan-Pakistan border gave the order for the attack but the target had still not been chosen when the men were arrested last year.
Three of the suspects were picked up in the cities of Dusseldorf and Bochum after allegedly buying bomb-making chemicals.
At the time, deputy federal prosecutor Rainer Griesbaum told reporters that the men had planned to set off a shrapnel-laden bomb in a crowded place such as on a bus, but the plot had still been "in the experimental phase".
Last September, two other men were arrested on suspicion of planning an Islamist bomb attack in Germany.