Chinese hackers are suspected of carrying out a “massive breach” affecting the data of millions of US government workers, officials said, the BBC reports.
The Office of Personnel Management (OPM) confirmed on Thursday that almost four million current and past employees have been affected.
The breach could potentially affect every federal agency, officials said.
Susan Collins, a member of the Senate Intelligence Committee, said it was thought to have originated in China.
The Chinese embassy in Washington warned against “jumping to conclusions”.
Embassy spokesman Zhu Haiquan told Reuters news agency that the accusations were “not responsible, and counterproductive”.