KYOTO, Japan  The demonstrators appeared one day in December, just as children at an elementary school for ethnic Koreans were cleaning up for lunch. The group of about a dozen Japanese men gathered in front of the school gate, using bullhorns to call the students cockroaches and Korean spies.

Inside, the panicked students and teachers huddled in their classrooms, singing loudly to drown out the insults, as parents and eventually police officers blocked the protesters’ entry.

The December episode was the first in a series of demonstrations at the Kyoto No. 1 Korean Elementary School that shocked conflict-averse Japan, where even political protesters on the radical fringes are expected to avoid embroiling regular citizens, much less children. Responding to public outrage, the police arrested four of the protesters this month on charges of damaging the school’s reputation.

More significantly, the protests also signaled the emergence here of a new type of ultranationalist group. The groups are openly anti-foreign in their message, and unafraid to win attention by holding unruly street demonstrations.