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 a 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.

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. It also said that Iwasaki's moves have constituted serious interference in China's internal affairs, and undermined its sovereignty and territorial integrity.

"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 said at a news conference in Beijing. "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.