THE HAGUE—This city is wrestling with a new generation of homegrown Muslim radicals, 10 years after a member of a local terrorist cell brutally killed Dutch filmmaker Theo van Gogh in Amsterdam.

More than a quarter of the 140 Dutch jihadists who the government says have traveled to Syria to join Islamic State were recruited in The Hague, making the city the Netherlands’ most important breeding ground for the extremist group.

The heightened Islamic radicalism now has invoked memories of the Hofstad Group, a small Islamic terrorist cell that was active in The Hague in 2003 and 2004. One of the group’s members, Mohammed Bouyeri, shot and stabbed Mr. van Gogh in a street in Amsterdam on Nov. 2, 2004, in the Netherlands’ first act of terrorism carried out in the name of Islam.

The Hofstad Group was dismantled after Mr. van Gogh’s killing and several members, including Mr. Bouyeri, were sentenced to prison. But some of the group’s early followers, then deemed too young to be a threat, now form the core of a new generation of Muslim radicals in The Hague, experts say.

The Hague promotes itself as the city of peace and justice, a reference to the International Court of Justice that is based here. But in some quarters of the city, young radical Muslims have their own nickname for the place: “Jihad city.”