A 28-year-old Moroccan man charged with helping the September 11 hijackers has gone on trial in the German city of Hamburg amid tight security. Mounir el-Motassadeq, the first alleged September 11 conspirator to stand trial anywhere, has told the court he knew nothing about any terrorist plot.

German prosecutors have charged Mr. Motassadeq with belonging to the militant cell in Hamburg that included three of the men believed to have been suicide pilots. They also accuse him of being an accomplice in the murder of the more than 3,000 people who perished in the September 11 attacks.

But although he admitted having close personal ties to such key cell figures as Mohammed Atta and Marwan al-Shehhi, Mr. Motassadeq insisted before the court that he was not aware of their plans to strike at U.S. targets.

The Moroccan man said he often prayed together with Mohammed Atta at a Hamburg mosque and that they discussed the Arab-Israeli conflict and the situation in Chechnya. But Mr. Motassadeq says his friend never spoke about resorting to violence.

Prosecutors say Mr. Motassadeq helped the September 11 plotters by, among other things, sending money to the U.S. bank account of Marwan al-Shehhi while he was taking flying lessons in Florida. They also say he attended an al-Qaida training camp in Afghanistan a year before the attacks were carried out.

The defendant's lawyers have acknowledged that their client did attend such a camp in Afghanistan but played down the significance of his stay there, saying that thousands of men had done the same thing without necessarily becoming involved in terrorist acts later.

Hamburg is regarded as having been a rear base for the plotters because Mohammed Atta, Marwan al-Shehhi and a third pilot, Ziad Jarrah, lived there for several years, as has Mr. Motassadeq. German officials have expressed unease at finding out that their country unwittingly harbored key perpetrators of the September 11 attacks.

Mr. Motassadeq was arrested last November. His trial is expected to go on for several months. If he is found guilty by the panel of five judges, he could receive a life sentence.