Schools in Charlottesville, Virginia, remained closed for a second consecutive day on Friday as police investigated a threat of racist violence against non-white students that had been posted online, officials said.

Police said early on Friday that they had arrested a 17-year-old suspect in connection with the threat. The teen, who has not been identified, was charged with making threats to commit serious bodily harm to persons on school property and online harassment.

City leaders have worked to ease racial tensions in the city since a white nationalist rally in August 2017 descended into violence, with a white nationalist killing a counterprotester, Heather Heyer, and injuring others after he drove into a crowd.

The threat against Charlottesville High School was reported to the police on Wednesday afternoon, according to the police department. The threat was reportedly made on 4chan, an anonymous online message board.

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School officials then quickly decided to close all schools in the city. According to US Census Bureau data, African Americans make up around 19 percent of Charlottesville’s population of nearly 50,000 people.

“We would like to acknowledge and condemn the fact that this threat was racially charged,” Charlottesville City Schools said in a letter sent to parents and posted on its website on Thursday evening notifying them of Friday’s closures. “The entire staff and School Board stand in solidarity with our students of colour.”

4chan, as well as other anonymous message boards, have become increasingly popular spaces for individuals to post racist and misogynistic comments and threats, as well as the planning of far-right events.

The man arrested in connection with the New Zealand mosque attacks in which more than 50 people were killed reportedly posted on a similar message board called 8chan.