Beijing has an ongoing spat with Tokyo over islands in the East China Sea claimed by both countries, and considers foreign criticism on sensitive political topics to be acts of interference.

Seki, a naturalised Japanese citizen, "spread false information, colluded with Japanese anti-China forces, and wantonly attacked and smeared China", foreign ministry spokesman Lin Jian told reporters on Monday.

"For his own selfish interests, (Seki) has forgotten his roots, betrayed his conscience, colluded with anti-China forces, and provoked trouble", Lin said.

"Betraying one's ancestors for personal glory will only lead to self-inflicted consequences."

The upper house member had violated the one-China principle which claims Taiwan as part of Beijing's territory, and "interfered in China's internal affairs", a separate Chinese foreign ministry statement said on Monday.

The ministry also cited visits by Seki, who is also known by his Chinese name Shi Ping, to the Yasukuni Shrine, which honours Japan's war dead including several World War II war criminals.

From Monday, China will freeze Seki's assets in the country, forbid Chinese entities from conducting transactions with him, and deny entry visas to him or his family.

A Japanese foreign ministry official told AFP it was the first time a Japanese politician had been sanctioned by the Chinese government.

Chief Cabinet Secretary Yoshimasa Hayashi said Tokyo had lodged a protest with China demanding it withdraw the measures.

"We cannot accept the Chinese side's decision, by citing Diet members' speeches, to take unilateral measures that appear to intimidate those holding differing positions," he told a regular news briefing.

"It is deeply regrettable from the perspective of Japan-China relations."

Seki was studying in Japan when Beijing cracked down on the 1989 Tiananmen Square demonstrations, an event which prompted him to ditch his native country, he told Japanese Japanese newspaper The Sankei Shimbun earlier this year.

Seki subsequently protested in front of the Chinese consulate general in Osaka, the newspaper said, calling for democracy in China.

In a post on X on Monday, Seki called the sanctions a "farce" and said he had no assets in China and no plans to visit the country.

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