TAIPEI/HONGKONG (Reuters) - Taiwan will step up its investigation of pro-Beijing newspapers accused by politicians on the self-ruled island of spreading fake news and surveillance activities that infringe national security, a security official said on Friday.

Claimed by Beijing as its sacred territory, Taiwan is China’s most sensitive issue, with President Xi Jinping having stepped up pressure on the island since 2016, when pro-independence leaning Tsai Ing-wen became its president.

Friday’s remarks follow reports in a Hong Kong-based tabloid, Wen Wei Po, which adopts a pro-Beijing stance, on the activities of several Hong Kong pro-independence activists who traveled to Taipei last week.

Along with another newspaper, the Ta Kung Pao, the tabloid is known for its aggressive reporting to hound democracy and independence activists in Hong Kong and Taiwan.

“The work on foreign hostile forces has been our top priority,” You Cheng-hua, the deputy director of a national security unit that reports to Taiwan’s Investigation Bureau, told reporters.

“We have been increasing our deployment and gathering intelligence.”

You added, “I also urge the public and media to help provide any tips on suspicious or illegal (activities).”

With Taiwan expected to hold a presidential election in about a year, Tsai has warned against Chinese efforts, including the deployment of “fake news”, to interfere with domestic politics and elections.

“Chinese media organizations are doing surveillance in Taiwan,” Lo Chih Cheng, a lawmaker from Tsai’s ruling Democratic Progressive Party, told reporters. “This has exposed a real national security problem.”

Lo, who sits on Taiwan’s Foreign and National Defense committee, added, “I’m worried that ‘red terror’ is happening in Taiwan...They are following Hong Kong people today. Will they follow Taiwanese tomorrow?”

Earlier, Alex Huang, a spokesman for Taiwan’s presidential office, said the Ta Kung Pao newspaper had engaged in “unlawful” acts through its surveillance of people, and added that it was spreading “fake news”.

The newspapers, Ta Kung Pao and Wen Wei Po, offered no immediate response to Reuters’ requests for comment.

One pro-independence Hong Kong activist who was followed and reported on, Tony Chung, told Reuters he and two members of his group, Student Localism, flew to Taiwan on Jan. 11.

The two newspapers on Monday detailed their meetings, movements, and even the books they browsed in a bookshop, along with photographs.

“The surveillance was very serious,” said Chung, a 17-year-old high school student. “It’s quite terrifying that even in Taiwan we’re followed 24 hours a day.”

Targets of the pro-Beijing media have also included those who are not citizens of Hong Kong or Taiwan.

In December, Wen Wei Po carried a front-page story on an Australia-based academic, Kevin Carrico, sending a team to follow him around during a visit to Hong Kong.

Carrico, who has done research on Hong Kong politics and the independence movement, was branded a “separatist” by the newspaper.