The US National Security Agency has been carrying out a cyberattack operation on the National Time Service Center over an extended period of time, China’s state security ministry said in a statement on its WeChat account on Sunday.

The ministry said it found evidence tracing stolen data and credentials as far back as 2022, which were used to spy on the staff’s mobile devices and network systems at the centre.

The US intelligence agency had “exploited a vulnerability” in the messaging service of a foreign smartphone brand to access staff members’ devices in 2022, the ministry said, without naming the brand.

The national time centre is a research institute under the Chinese Academy of Sciences that generates, maintains and broadcasts China’s standard time.

The ministry’s investigation also found that the United States launched attacks on the centre’s internal network systems and attempted to attack the high-precision ground-based timing system in 2023 and 2024.

The US embassy in Beijing did not address the accusations directly but said cyber actors based in China have compromised major US and global telecommunications providers’ networks to conduct broad significant cyber espionage campaigns.

“China is the most active and persistent cyber threat to US government, private-sector, and critical infrastructure networks,” an embassy spokesperson told Reuters in an email.

China and the US have increasingly traded accusations of cyberattacks in the past few years, each portraying the other as its primary cyber threat.

The latest accusations come amid renewed trade tensions over China’s expanded rare earths export controls, and the US threatening to further raise tariffs on Chinese goods.