BEIJING (AP) — China’s government tightened control over popular instant messaging services Thursday after telling South Korea access to some foreign services was blocked because they were used to exchange terrorism-related information.

The government announced that only established media companies will be allowed to release political and social news. That would curtail a growing trend in use of instant messaging services by journalists and scholars to distribute independent news reports and commentary.

The ruling Communist Party has repeatedly tightened controls over microblogs and other social media that give Chinese a rare platform to express themselves to a large audience in a country where all traditional media are state-owned.

Meanwhile, China has informed South Korea it has blocked access to Kakao Talk and Line, two mobile messaging services, which it said were used to exchange terrorism-related information, according to a South Korean official who asked not to be named because he was not authorized to speak on the matter.

Beijing is on edge about security following a series of deadly attacks communist authorities blame on Islamic radicals it says want independence for the country’s northwestern region of Xinjiang.

Beijing says it has confirmed terrorism-related information circulated through Kaokao Talk and Line, the South Korean official said. It was not clear how Beijing had access to messages between users of the two services, which are private and seen only by the participants.

Chinese authorities gave no details of what terrorists might use the message services, the official said. He declined to give more details.

In May, the government launched a one-month crackdown on instant messaging services to stop what it called the “infiltration of hostile forces.” Authorities said it targeted people spreading rumors and information about violence, terrorism or pornography.

The campaign targeted public accounts on services including WeChat in China, a mobile message service run by Tencent Holdings Ltd., which has surged in popularity in the last two years.

Canny Lo, spokeswoman for Tencent, said the company complies with the government policies where it operates and endeavors to provide a healthy and secure online environment for users.

“Our information management does not allow for any blank space. It would be regulated later or sooner, and it is only a matter of time,” said Hu Yong, professor with the School of Journalism and Communication at Peking University and an expert on the Internet.

Last summer, Beijing cracked down on microblogging services such as Sina Weibo in an apparent effort to stifle criticism of the ruling party. Authorities closed accounts of liberal-minded microbloggers and detaining bloggers on criminal charges of spreading rumors or other offenses.

The crackdown helped drive users to WeChat, which allows individuals to set up public accounts that others can subscribe to, similar to the microblogging feature of having followers but without a word limit.

Journalists and scholars have since set up accounts and attracted sizeable followings on WeChat.

Those public accounts have created a new venue for information-sharing, and now “the government needs to block the content which it deems ‘harmful’,” Hu said.

Compared to its response to microblogging, Beijing has reacted faster to WeChat and similar services. Government agencies and state media have set up public accounts and censors remove accounts deemed offensive.

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AP Technology Writer Youkyung Lee in Seoul and researcher Yu Bing in Beijing contributed.