At least 17 historically Black colleges and universities said they received bomb threats in the past two days, though no explosives have been found.
A series of unconfirmed bomb threats disrupted life at more than a dozen college campuses this week, drawing the attention of the White House and the F.B.I.
Of particular concern were the threats directed at historically Black colleges and universities, or H.B.C.U.s, including at least 17 that temporarily canceled in-person classes and locked down buildings.
President Biden was aware of the threats, Jen Psaki, the White House press secretary, said at a news conference on Monday.
“I will say that these are certainly disturbing,” Ms. Psaki said. “And the White House is in touch with the interagency partners, including federal law enforcement leadership, on this.”
The F.B.I. said in a statement that it was “working with our law enforcement partners to address any potential threats.”
The authorities have so far not described any of the threats as credible. But school officials at many of the universities took precautions, such as sweeping campus buildings and moving to remote instruction. Some of the H.B.C.U.s have received multiple threats this year.
Representative Val B. Demings, Democrat of Florida and a former police chief, said on Twitter on Monday that the threats against historically Black colleges “demand a response.”
“As a former law enforcement officer I’ll keep working to make sure our institutions and law enforcement have the resources they need to keep all of our students and communities safe,” Ms. Demings said.
On Monday, at least seven H.B.C.U.s, including Southern University and A&M College in Baton Rouge, La., and Delaware State University in Dover, Del., received bomb threats.
At least 10 other historically Black colleges, including Spelman College in Atlanta, reported threats on Tuesday, the first day of Black History Month. The threats were made in the early hours of the day, according to several affected schools.
At least four schools issued “all clear” messages by midday Tuesday, including Kentucky State University; Howard University in Washington, D.C.; and Jackson State University and Tougaloo College in Jackson, Miss.
Separately on Tuesday, U.C.L.A. said that all of its classes for the day would be remote “out of an abundance of caution” after some school staff received threats from a specific person. The school said that, according to law enforcement officials, the person was not in California and was “under observation.”
Investigations were still underway on Tuesday morning at several of the historically Black colleges, including those that had received repeated threats this year.
“The threats are despicable,” Mary Schmidt Campbell, president of Spelman College in Atlanta, said in an email to students and staff members on Tuesday. “They are designed to make us feel fearful and vulnerable.”
In a letter to Howard students and staff members on Monday, Marcus Lyles, the school’s chief of police, said that while the recent threats against the university had not been credible, they were “a drain on institutional and municipal resources and an unnecessary mental burden on individuals trying to learn and work on our campus.”
At least eight H.B.C.U.s had also received threats on Jan. 5. Many campuses were nearly empty because of winter break and the coronavirus pandemic, but dorm rooms and administrative buildings were still cleared out.
A week later, the University of Utah reported that its Black cultural center had also received a bomb threat.
The recent bomb threats at historically Black colleges and universities followed a series of unsubstantiated threats in November at several Ivy League schools as well as campuses in Ohio and California. Those threats were later deemed not to be credible.
Eduardo Medina contributed reporting.
