Beijing accused the United States on Thursday of smearing China after Washington alleged Chinese hackers were attempting to steal research on developing a vaccine against the coronavirus.
The claims have added fuel to tensions between the global superpowers, who have traded barbs over the origin of the pandemic that has killed 300,000 people.
China expresses strong dissatisfaction and firm opposition to such smearing
US authorities said Wednesday that Chinese hackers were trying to obtain coronavirus data on treatments and vaccines, warning the effort involved Chinese government-affiliated groups and others.
The FBI and the Cybersecurity and Infrastructure Security Agency said China's efforts posed a "significant threat" to the US response to COVID-19.
"China expresses strong dissatisfaction and firm opposition to such smearing," foreign ministry spokesman Zhao Lijian told a regular press briefing.
"Judging from past records, the US has carried out the largest cybertheft operations worldwide," Zhao said.
He stressed that Beijing has significant achievements of its own in the fight against the pandemic.
China is "also leading the world in COVID-19 vaccine research and treatment", and therefore has more reason to worry about cyber espionage itself, Zhao said.
He added that the country has cracked down on cyber-hacking, and that any cyberattack hindering the global fight against the pandemic should be condemned by people around the world.
Responding to US president Donald Trump's reference to COVID-19 as the "Plague from China", Zhao said the US should stop blaming and discrediting others, and focus on their own prevention and control work.
The virus first emerged in the central Chinese city of Wuhan late last year.