WASHINGTON — Attorney General William Barr vowed Tuesday that there would be swift and severe action if a foreign government is behind disinformation campaigns aimed at spreading fear in the U.S. amid the coronavirus pandemic or a denial of service attack on the networks of the Department of Health and Human Services. “Our primary role right now is to investigate,” Barr said. “The FBI is very active, trying to determine who is responsible for these things.”

U.S. national security officials said Monday there had been a “cyber incident” involving the computer networks of the Health and Human Services Department, but the networks were operating normally. They didn’t detail the scope of the incident, but HHS Secretary Alex Azar later said the networks were not penetrated and that the department has taken strong defensive action.

A denial of service attack occurs when a perpetrator trying to make a network unavailable to its intended user temporarily disrupts internet connections.

It came just days after federal officials began confronting what they said was a deliberate effort by a foreign entity to sow fears of a nationwide quarantine. Agencies took coordinated action Sunday evening to deny that any such plans were put in place, as they tried to calm a nation already on edge by disruptions to daily life caused by the coronavirus.