RICHMOND, Va. (Reuters) - Schools in a Virginia county closed on Friday as a safety precaution after a class assignment asking students to practice Arabic calligraphy using a Muslim statement of faith sparked an angry outcry from parents and threats against school officials.

Augusta County Public Schools officials said no specific threat had been made against students, but some calls and emails received by the district posed a risk of harm to school officials.

The outcry appeared to reflect anxiety and distrust of Muslims among some Americans following a Dec. 2 shooting that killed 14 people in San Bernardino, California, by a married couple inspired by militant Islamism and attacks in Paris by Islamic State militants on Nov. 13 that killed 130 people.

Some messages to the Virginia school district contained profane and graphic content, including a call to behead the teacher who gave the assignment, Augusta County Sheriff Randy Fisher said.

Others threatened large protests on or near school property in the district, located in Virginia’s Shenandoah Valley about 150 miles (240 km) southwest of Washington, officials said.

The Arabic text, according to the News Leader newspaper, translated as “There is no God but Allah, and Mohammad is the messenger of Allah.”

Some parents have accused the teacher, Cheryl LaPorte, of trying to indoctrinate students with Islam and are calling for her to be fired.

“I do not trust her to teach my son and regardless of the outcome he will not sit in her classroom,” mother Kimberly Herndon said in a Facebook post that has been shared more than 300 times.

The district decided to begin the school system’s winter break early and canceled extracurricular activities this weekend for the district’s 10,000 students, Superintendent Eric Bond said in a statement.

Across the country this week, a rash of email and phone threats of violence hit schools. Most were deemed not credible and schools opened.

Los Angeles officials closed the country’s second-largest public school system on Tuesday after receiving emailed threats that were later deemed a hoax, a move that was criticized by some as overreaction.

Franklin Community Schools in Indiana were shut on Friday after a high school was evacuated a day earlier due to a threat.

The Federal Bureau of Investigation was assisting in the investigation of threats that caused suburban Indianapolis school districts in Plainfield and Danville to cancel classes on Thursday.

The Virginia school district said students would continue to learn about world religions as required by the state but a non-religious sample of Arabic writing would be used in the future.

“No lesson was designed to promote a religious viewpoint or change any student’s religious belief,” the statement said.

LaPorte said she had received overwhelming support from former students, colleagues and others in the community. A “Support LaPorte” page on Facebook had more than 2,000 members on Friday.

“All I want now is time for our community to heal,” she said in an email to Reuters.