But French security experts and counterterrorism judges have also argued that leaving nationals in the camps incurs greater risks than bringing them home, because they could join a resurgent Islamic State in the region.

But the court on Wednesday ruled that “there were special features which enabled France’s jurisdiction” over the family members, including that their lives were at risk, that several requests for repatriation had been sent to the French authorities and that Kurdish forces had long called for their return home.

During the public hearing, held in September, the lawyer for the French government argued that it should not be obliged to repatriate, as it had no control or authority over its citizens in northeastern Syria. France was supported in its argument by seven other European countries, demonstrating the far-reaching nature of the case

PARIS — Europe’s top human rights court condemned the French government on Wednesday over its refusal to bring home the families of two Islamic State fighters, a landmark ruling that may push France and other European countries to speed up the repatriation of nationals held for years in squalid detention camps in northeastern Syria.