Two Chinese nationals have been indicted for seeking to steal COVID-19 vaccine research and intellectual property from hundreds of companies in the United States and other countries, the US Justice Department said Tuesday.

Li Xiaoyu, 34, and Dong Jiazhi, 33, also targeted human rights activists in the United States, China and Hong Kong, Assistant Attorney General for National Security John Demers said.

The hackers, who are believed to be in China beyond the reach of US law enforcement, acted in some instances "for their own personal gain" and in others for the benefit of China's Ministry of State Security, Demers said at a press conference.

"Cybercrimes directed by the Chinese government's intelligence services not only threaten the United States but also every other country that supports fair play, international norms, and the rule of law," FBI Deputy Director David Bowdich said.

US Attorney William Hyslop said the hackers targeted companies worldwide.

"The computer systems of many businesses, individuals and agencies throughout the United States and worldwide have been hacked and compromised with a huge array of sensitive and valuable trade secrets, technologies, data, and personal information being stolen," Hyslop said.

The Justice Department said the targets of the hackings included "hundreds of victim companies, governments, non-governmental organizations, and individual dissidents, clergy, and democratic and human rights activists in the United States and abroad, including Hong Kong and China."