Dutch detectives are investigating more than 200 Dutch jihadis who have gone to fight in Syria and Iraq, public prosecutor Ferry van Veghel told a court in Rotterdam on Thursday.

The aim is to ensure they can be jailed as soon as they return to the Netherlands, Van Veghel said at a pro-forma hearing in the case of 10 jihadi suspects.

The 200 investigations currently underway are time-consuming and intensive to deal with because of the difficulty in collecting evidence, Van Veghel is quoted as saying by broadcaster RTL. Nor is it possible to collect physical evidence because the men are all abroad.

The 10 facing charges at the Rotterdam court range in age from 18 to 29 and come from all over the country, including Arnhem, Almere, Rotterdam, Utrecht and Zoetermeer. Their number includes Dutch Muslim convert Victor Droste.

Last year, four jihadis were jailed for up to six years in absentia, in what the department sees as an important precedent.