TOKYO (AP) — China announced Monday that it is sanctioning a conservative Japanese lawmaker close to Prime Minister Sanae Takaichi, accusing him of “colluding with” separatists in Taiwan, the latest incident that underlines growing tensions between Tokyo and Beijing over the self-governed island.

Japan called the step unacceptable and regrettable and demanded that China retracts it immediately.

“The one-sided action taken by China as if to intimidate those of different views than its own is absolutely unacceptable,” Japan's Deputy Chief Cabinet Secretary Masanao Ozaki said. “It is extremely regrettable from the perspective of the Japan-China relations.”

China's Foreign Ministry earlier said the sanctions include banning the entry of Keiji Furuya to China, including to Hong Kong and Macao, and prohibiting his activities with organizations and individuals in China, effective immediately.

Furuya heads a bipartisan Japan-Taiwan lawmakers' consultation council and has visited Taiwan regularly. He most recently visited Taiwan's capital of Taipei, where he held talks with Taiwanese President Lai Ching-te in mid-March.

Furuya is a close ally of Takaichi who headed the election strategy for their governing Liberal Democratic Party ahead of the party’s electoral victory in February.

China accused Furuya of repeatedly visiting Taiwan despite China's strong opposition and of “colluding with Taiwan independence separatist forces."

The ministry said Furuya's activities violate the one-China principle — which holds that Taiwan is a province of China — and “grossly interfere in China's internal affairs and seriously undermine China's sovereignty and territorial integrity."

“The Taiwan question is at the core of China's core interests, as well as the red line that must not be crossed,” Chinese Foreign Ministry spokesperson Mao Ning said in Beijing.

Furuya said the notice came via the Japanese Foreign Ministry. He defended his actions, telling reporters that “it is only natural” for parliamentary groups to promote exchanges between “countries" with shared values.

Furuya said he had not visited China for decades and had no personal assets in that country, “so I don't think there is any impact” from the sanctions.

The move marks the latest example of growing tensions between Beijing and Tokyo since Takaichi infuriated Beijing last November by saying a hypothetical Chinese military action against Taiwan would amount to a “survival-threatening situation” for Japan that would justify Japanese troop engagement.

The comment broke with Japan’s past vague stance on how Japan would respond if China used force against the island.

China views Taiwan as its internal matter and opposes any foreign involvement in the island, and it reacted with a range of diplomatic and economic steps.

Mao, China's Foreign Ministry spokesperson, said Furuya ignored China’s repeated reminders of its position following Takaichi’s “erroneous remarks on Taiwan” and said that the sanctions are meant “to serve as a warning to others."

China last year also sanctioned a Chinese-born and naturalized Japanese opposition lawmaker, Seki Hei, for allegedly “spreading fallacies” about Taiwan and other disputed territories.