Sydney school scrawled with IS slogans

Spray-painted pro-Islamic State slogans have been removed from buildings at a boys high school in Sydney's southwest.

Police are investigating after messages such as "ISIS R coming" and "ISIS beheads" were scrawled over four buildings at East Hills Boys High School, on Lucas Road, Panania.

They say vandals wrote the messages overnight on Tuesday and they were discovered by a teacher on Wednesday morning.

"It's intimidating, it's harassing and it's against the law," Inspector Scott McAlpine told the Seven Network.

The Department of Education says the graffiti has been removed and that the school does not tolerate this behaviour.

Earlier this year, the high school came to the attention of authorities when two students refused to stand for the national anthem, as reported in News Ltd newspapers.