Fliers saying "it's okay to be white" were found taped to the exterior doors of a Maryland high school Wednesday morning, apparently as part of an effort to spark racial division.

The principal at Montgomery Blair High School in Silver Spring sent a letter home to families informing them that the signs were discovered on 10 doors at 5:45 a.m. and removed by staff before students arrived for ­classes.

"We are taking this seriously and are investigating this incident," wrote Renay Johnson, the school's principal. "Our research so far has indicated that this may be part of a concerted national campaign to foment racial and political tension in our school and community. The same flier was posted in other cities and communities this week."

Johnson described the school community as "smart, diverse and inclusive" and said it would not "fall victim to attempts to divide us."

"We are committed to providing a safe and welcoming environment for every student," the principal's letter said.

Stickers bearing the same message were discovered Wednesday morning on light poles and electrical boxes in Cambridge, Mass., according to a report in the Boston Globe. Similar signs were found on the campus of Tulane University in New Orleans, and in Rocky River, Ohio.

The fliers appear to be part of an online campaign that is detailed on the Web forum 4chan. It directed that the posters should be displayed Halloween night on campuses and elsewhere, and discouraged vandalism.

At the University of Alberta in Canada, one of the posters appeared Tuesday outside the school's Native Studies department, according to a media report. That came a day after a racist jack-o'-lantern was left outside the same academic office.

"Messaging or displays that target or marginalize any individuals or groups will not be tolerated," the president of the University of Alberta, David Turpin, said in a statement.