By
Laurence Norman

Updated Aug. 11, 2014 11:18 a.m. ET

Kosovo launched a major operation Monday morning against suspected domestic militants who have fought in Syria and Iraq, arresting at least 40 people and seizing weapons and explosives in dozens of locations, authorities said.

The move is the biggest action yet against suspected militants in Kosovo, where the government has long played down concerns about the threat posed by extremists.