At least a dozen historically Black colleges and universities in the United States received bomb threats and put their campuses on lockdown on Tuesday, a day after a rash of similar threats forced several of them to cancel classes.
The threats in cities from Baltimore to New Orleans coincided with the first day of US Black History Month.
"We don't think it's by coincidence that we received this particular threat at this particular time," said A. Zachary Faison, Jr., president of Edward Waters University in Jacksonville, Florida.
A 3:30 a.m. caller to the Jacksonville sheriff's office warned that "multiple explosive devices" had been placed around the campus and would be detonated 12 hours later, followed by a school shooting, Faison said.
Local law enforcement officers with dogs were patrolling the campus as of midday on Tuesday, he said. The Jacksonville sheriff's office declined comment.
In a statement the FBI said it was aware of the bomb threats and working with its law enforcement partners to address potential threats. It encouraged members of the public to report anything suspicious to the bureau.
White House press secretary Jen Psaki told a press briefing that "we take these threats incredibly seriously," but said the White House still did know what had motivated the threats.
The U.S. intelligence community warned months ago of a threat that racially motivated violent extremists, such as white supremacists, would seek to carry out mass-casualty attacks on civilians.
Howard University in Washington, Morgan State University in Maryland, Spelman College in Georgia and Xavier University of Louisiana were among the colleges that received threats, according to Twitter posts and statements from the schools.
"Institutions in the Black community become targets when issues of race, issues of civil rights, issues of equality bubble to the surface and become the focal point of American society," said Howard University librarian Lopez Matthews, Jr.
Matthews said Howard University came under threat from racist attackers during riots in Washington in 1919, and again in the 1960s during the U.S. civil rights movement.
Howard gave the all clear a few hours after the campus received a threat at around 2:55 a.m., but not all students were reassured.
"We will not let (the threats) deter us from fulfilling our mission of providing superior educational experiences to our students," Howard University said in a statement.
Half of Caleb Brown's classmates were absent from his film-directing class on Tuesday morning, the Howard senior told Reuters in an interview.
"For just today and tomorrow, if we could have gone virtual and they could have brought in a team to sweep every building on campus from top to bottom to really check and make sure that campus is safe, I would feel more at ease," said Brown, 22, a television and film major.
By noon on Tuesday, at least six of the colleges that received threats had investigated them and issued "all clear" messages, though some, including Spelman and Tougaloo College in Mississippi, were still holding class virtually for the day.
On Monday, several of the colleges told students and staff to shelter in place and canceled classes for the day after similar bomb threats. Authorities said they did not find any suspicious devices, allowing the schools to reopen.