An American airstrike killed an Iran-backed militia leader in Baghdad on Thursday, U.S. officials said, drawing denunciations from Iraqi leaders and a vow from the militant group to retaliate, amid already metastasizing tensions in the region.

A U.S. official said Washington conducted a “precision strike” on a vehicle traveling in eastern Baghdad, targeting a member of the Harakat al Nujaba group that the U.S. has been tracking. The Pentagon didn’t immediately respond to a request for comment.