Taipei, Feb. 26 (CNA) Premier Su Tseng-chang said Friday that the recent news reports of the Taiwan government spying on foreign envoys and opposition figures were part of a "cognitive warfare" effort by outside forces.

The phrasing and Chinese characters used in a letter cited in the news stories were a red flag, Su told reporters, on his way to a legislative hearing.

"Our citizens and relevant government agencies do not say things that way," Su said.

"Unscrupulous people from outside" probably want to damage Taiwan's relations with its allies through disinformation campaigns, he said.

He was responding to questions about a letter received recently by several Taiwanese media organizations, which claimed that the National Security Bureau (NSB) and the Ministry of Justice Investigation Bureau (MJIB) had been wiretapping members of the diplomatic corps in Taiwan, government and military officials, and media personalities, especially those affiliated with the opposition parties.

The letter listed the names of some of the alleged targets, including people at the American Institute in Taiwan and the Japan-Taiwan Exchange Association, and opposition Kuomintang (KMT) Chairman Johnny Chiang.

The sender claimed to be a long-serving officer at the National Security Bureau, Taiwan's top intelligence agency.

In a statement issued Thursday evening, the NSB said the letter was aimed at creating social conflict within Taiwan and sowing distrust between the country and its friends.

The wording of the letter showed terms commonly used by mainland Chinese, such as the translated names of some countries and institutions, the NSB said.

There were also indications that some of the characters had been converted from simplified to traditional Chinese via a computer program, the NSB said.

Simplified Chinese characters are used in mainland China, while Taiwan uses traditional Chinese, the bureau noted.

Apart from the anonymous letter, the NSB said, it found that some people had been using fake social media accounts to spread misinformation in Taiwan in recent years.

"Investigations showed that these were actions by outside forces to wage cognitive warfare against Taiwan," the bureau said, urging the public not to be misled by fake news.

Cognitive warfare is defined by some security analysts as an influence campaign that manipulates trusted information to change the target's views and advance the initiator's interest.