Several black colleges and universities in the United States received bomb threats Tuesday and locked down their campuses. A day after a series of similar threats caused classes at other schools to be canceled for the day.

Howard College in Washington, the College of the District of Columbia, Kentucky State, Xavier College of Louisiana and Fort Valley State in Georgia were among the schools that received threats, according to Twitter postings and local media.

“Campuses are currently on lockdown. Students remain in residence halls. Non-residential students and staff should remain on campus until further notice NOT. Campus operations are suspended for today,” Fort Valley State shared in a tweet.

Howard gave the all-clear Tuesday morning after the campus received a threat around 2:55 a.m., according to Twitter.

The bomb threats occurred after several other HBCUs on Monday told students and staff to get to safety and canceled classes for the day after receiving similar threats. Authorities said they found no suspicious devices, allowing the schools to reopen.

“The FBI is aware of the series of bomb threats across the country and we are working with our law enforcement partners to address potential threats,” the FBI said in a statement Tuesday. It urged the public to report anything suspicious to the office.

Students at Xavier College in Louisiana were told to stay in their dorms and monitor college channels until further notice.

“ALERT! XULA has received a bomb threat and is working with authorities. The campus will be on lockdown until 12 a.m.,” the school announced in a tweet.