China announced countermeasures on Monday against a former senior official of Japan's Self-Defense Forces for colluding with "Taiwan independence" separatist forces, and stressed that the Taiwan question is the red line that must not be crossed.

According to a decree released by the Foreign Ministry, the sanctions, which took effect on the same day, include freezing movable and immovable properties and all other types of assets in China of Shigeru Iwasaki, former chief of the Joint Staff of Japan's Self-Defense Forces.

Organizations and individuals in China are prohibited from conducting transactions or cooperating with Iwasaki, who will not be issued Chinese visas or allowed to enter China, including the Hong Kong and Macao special administrative regions.

The sanctions were imposed according to China's Anti-Foreign Sanctions Law, because Iwasaki has seriously violated the one-China principle and the four China-Japan political documents by openly colluding with "Taiwan independence" separatist forces, the ministry said in the decree. It also said that Iwasaki's moves have constituted serious interference in China's internal affairs, and undermined its sovereignty and territorial integrity.

In March, China said it had lodged protests with the Japanese side, following news that Iwasaki was taking the post as a "political consultant" for the Taiwan authorities.

"The Taiwan question is at the core of China's core interests and is the red line that must not be crossed," Foreign Ministry spokesman Guo Jiakun emphasized at a daily news conference in Beijing on Monday. "China firmly opposes Iwasaki taking the post of the so-called 'political consultant' of the Taiwan authorities."

China has protested to the Japanese side more than once, but the former Japanese senior official refused to reflect on and correct his wrongdoings, Guo said.

"Instead, he has continued to collude with 'Taiwan independence' separatist forces and make provocations," Guo said, adding that his egregious moves triggered the sanctions.

The sanctions came amid rising tensions in relations between China and Japan, caused by the erroneous remarks made last month by Japanese Prime Minister Sanae Takaichi, which implied military intervention in a "survival-threatening situation" involving China's Taiwan region.

Da Zhigang, a researcher at the Heilongjiang Provincial Academy of Social Sciences' Institute of Northeast Asian Studies, said that just like Takaichi has not yet retracted her remarks, Iwasaki working for the Taiwan authorities shows that the Japanese side has not lived up to the commitments it made in the four China-Japan political documents.

The fact that the retired senior official of Japan is working directly for the Taiwan authorities is not only egregious in nature, but also poses great risks for peace across the Taiwan Strait, Da said. This also demonstrates Japan's attempts to hollow out the one-China principle, he added.

wangqingyun@chinadaily.com.cn