The U.S. Department of Justice said Wednesday that American prosecutors had charged four personnel of China's Ministry of State Security with spying on U.S.-based human rights advocates.

According to an indictment unsealed Tuesday, the intelligence officials collaborated with a U.S. citizen to carry out the campaign, instructing him to meet with human rights activists and dissidents, report on their activities and ideas, and send along their personal information.

The accusations stem from the case against Wang Shujun, a U.S. citizen who was arrested in March and accused with operating as a Chinese agent and making false statements to U.S. officials.

While the earlier criminal complaint outlined Wang's handlers' acts, they were neither named nor included as defendants.

Tuesday's indictment named Feng He, Jie Ji, Ming Li, and Keqing Lu as the four state security officers still at large.

Based on the accusation, Li and He operated from the State Security Bureau in Guangdong, while Ji and Lu operated from Qingdao in Shandong province.

Wang allegedly acted "under the direction and supervision" of China's Ministry of State Security between 2005 and 2022, connecting with his handlers via a messaging app and face-to-face talks during travels to China.

The indictment said that these journal entries were occasionally saved as email drafts, allowing the handlers to access the email account and examine the material without the need for messages to be sent.

In a 2016 journal post, Wang allegedly revealed the identity of an individual organising protests against the forthcoming U.S. visit of Chinese President Xi Jinping.

Wang is said to have recounted his conversations with an unnamed, renowned Hong Kong dissident at Li's request in a later diary post, including comments about the activist's views on Hong Kong politics and personal information such as his home phone number.

Later in 2019, the dissident, identified in the indictment as a "well-known attorney" and former member of Hong Kong's legislative council, was detained and accused for his role in organizing a demonstration.

In recent months, the administration of President Joe Biden has increased its examination of purported Chinese government tactics to intimidate its critics abroad.

In addition to the allegations against Wang, the Department of Justice in March also charged a number of Chinese and American nationals with targeting Chinese government critics.