Thirteen men suspected of having links to al-Qaeda have gone on trial in the Dutch city of Rotterdam.
Al-Qaeda is blamed for the 11 September 2001 attacks in the US
Twelve of the men were living in the Netherlands illegally when they were arrested last year.
Prosecutors have accused them of helping the enemy in a time of conflict - a charge which has not been used in the Netherlands since crimes related to World War II.
But the long-dormant charge became an issue as soon as the trial began, with the defence claiming it was a war crimes charge and should be heard in a military court.
The judge decided a civil court was the place to hear it first. Prosecutors say the law in question refers to armed conflict and not war.
However, the BBC's Geraldine Coghlan at the trial says there could still be problems establishing evidence of the Dutch role in the conflict cited, the US-led war against the Taleban and al-Qaeda in Afghanistan.
The suspects come from countries including Libya, Egypt, Algeria, Morocco, Iraq and Turkey.
They are charged with providing financial and logistical support for al-Qaeda, the radical Algerian Salafist group, the GSPC, and other militant Islamic groups.
The 12 men listened through headphones to an Arabic translation of the proceedings, speaking only to confirm their names and dates of birth.
Prosecutors claim they were recruiting young volunteers for the jihad, or holy war, against the West.
But Islamic experts called to the witness box were unable to establish whether documents found at the suspects' homes were a call to war or indicated a personal spiritual struggle.
The prosecution suffered another setback when the deputy head of Dutch intelligence said that he was constrained by a code of secrecy from telling the court how information on the suspects was obtained.
The trial will also examine alleged links to the deaths of two young Dutchmen of Moroccan origin last year.
They were killed in clashes with Indian forces in Kashmir where they were on an apparent suicide mission.
The Dutch secret service estimates that more than 100 terrorist operatives are at work in the Netherlands.
But prosecutors lost their first major terrorism case here in December.
The court acquitted four suspects accused of plotting to attack the United States embassy in Paris because of insufficient evidence.
This time, our correspondent says, prosecutors hope to bolster their case with echoes of Nazi occupation, by resurrecting the charge of helping the enemy in a time of war.