A riot police officer dispatched from Osaka to help local police respond to anti-base protests in Okinawa Prefecture hurled an ethnic slur at protesters, calling them dojin, meaning aboriginal, police officials said Wednesday.

The incident came amid intensifying confrontations between riot police and local residents over the construction of helipads at a U.S. military training site in the northern part of the prefecture.

Shortly before 10 a.m. on Tuesday, several protesters were pushing on a fence near a gate to the Northern Training Area straddling the villages of Kunigami and Higashi as more than a dozen riot police officers on the opposite side of the fence warned them to desist.