The chief of the top U.S. domestic intelligence agency has claimed that North Korea attempted to hack into systems containing  data on the nation's COVID-19 vaccine technology.

FBI Director Christopher Wray made the claim in a report submitted to a hearing of the Senate Judiciary Committee on Thursday.

He said the U.S. has publicly called out the North, China and Russia for “using cyber operations to target U.S. COVID-19 vaccines and research.”

He went on to say that Washington has, in the past year, seen cybercriminals target hospitals, medical centers and educational institutions for theft or ransomware, adding that such moves disrupted computer networks and systems, increasingly endangering patients’ lives.

The FBI chief stressed the need to “make it harder and more painful for malicious cyber actors and criminals to do what they are doing.”

Wray’s comments come roughly a month after U.S. security authorities issued a joint warning that North Korean state-sponsored hackers may target hospitals and other health care facilities in the U.S. using ransomware.

The Federal Bureau of Investigation, the Treasury Department and the Cybersecurity and Infrastructure Security Agency issued the joint warning.

In the warning, the agencies said North Korean hackers have been using Maui ransomware since at least May 2021 to target healthcare and public health sector organizations.