Chinese hackers targeted Uyghur activists and journalists living in the United States in an attempt to spy on them, an investigation by security staff at Facebook has found.

“They targeted activists, journalists and dissidents among Uyghurs and other Muslim minorities from Xinjiang in China primarily living abroad in Turkey, Kazakhstan, the United States and other countries,” Facebook said in a post Wednesday detailing its findings about the cyber espionage campaign.

The hackers infected targets’ electronic devices with malware “to enable surveillance,” Facebook (FB) said. In some cases, the hackers compromised or impersonated news websites popular among Uyghurs to secretly install spying software.

“This group used fake accounts on Facebook to create fictitious personas posing as journalists, students, human rights advocates or members of the Uyghur community to build trust with people they targeted and trick them into clicking on malicious links,” the company said.

In January, the United States officially determined that China is committing genocide and crimes against humanity against Uyghur Muslims and ethnic and religious minority groups who live in the northwestern region of Xinjiang. (The Chinese government denied this assertion, calling it a lie.)

The US State Department has previously estimated as many as 2 million Uyghurs, as well as members of other Muslim minority groups, have been detained in internment camps in the region.

Facebook did not point the blame directly at the government in Beijing but said the hackers “had the hallmarks of a well-resourced and persistent operation.” (Hackers linked to the Chinese government previously hacked iPhones and Android devices to target Uyghurs.)

The hacking groups identified as being behind the latest campaign are known in the cybersecurity industry as “Evil Eye” and “Earth Empusa” and have been involved in previous spying campaigns, according to Facebook.

Facebook's announcement comes a day before CEO Mark Zuckerberg is set to appear before Congress, alongside the heads of Twitter and Google. Zuckerberg is expected to be asked about the role his platform may have played in fueling the January 6th riot at the US Capitol, among other issues.

Facebook and other social media platforms were widely criticized for allowing Russian trolls to pose as Americans online in the run-up to the 2016 election. Since then, Facebook has publicly called out some governments and other entities it finds using its platform for nefarious purposes.