U.S. special forces captured the head of the Islamic State group’s unit trying to develop chemical weapons in a raid last month in northern Iraq, Iraqi and U.S. officials told The Associated Press, the first known major success of Washington’s more aggressive policy of pursuing ISIS militants on the ground.

The Obama administration launched the new strategy in December, deploying a commando force to Iraq that it said would be dedicated to capturing and killing ISIS leaders in clandestine operations, as well as generating intelligence leading to more raids.

U.S. officials said last week that the expeditionary team had captured an Islamic State leader but had refused to identify him, saying only that he had been held for two or three weeks and was being questioned. […]