Japanese Deputy Prime Minister Taro Aso said Japan and the U.S. would have to defend Taiwan together in the event of a major problem, Kyodo News reported, marking some of the highest-level remarks from Tokyo on the sensitive subject, Bloomberg reports.

In comments at a political fundraising party in Tokyo on Monday, Aso said an invasion of Taiwan by China could be seen as an existential threat, allowing Japan to exercise the right to collective self-defense, Kyodo reported.

Japan has sought to avoid alienating China, its biggest trading partner, while maintaining its alliance with the U.S., amid tensions between the world’s two largest economies over topics ranging from the origins of the coronavirus disease to human rights.

Recent comments about Taiwan by some Japanese officials have nonetheless angered China, which sees Taiwan as part of its territory. China has also turned up the heat.

President Xi Jinping struck a defiant tone in a speech marking the Communist Party’s 100-year anniversary last week, calling China’s quest to gain control of Taiwan a “historic mission” and warning the country’s adversaries to avoid standing in the way of his government.

Japanese Vice Defense Minister Yasuhide Nakayama said in a presentation to a Washington think tank last month that China presented a growing threat, and it was necessary to protect Taiwan as a “democratic country.”

Chinese officials urged Japan to disavow the remarks, which they described as sinister, irresponsible and dangerous.

Japan’s top government spokesman, Katsunobu Kato, said the comments represented a personal view, while Defense Minister Nobuo Kishi said there was no change to Japan’s support for the “one China” policy, under which Taiwan is not treated as a country, TBS news reported.

Tensions have risen around Taiwan in recent months, with China sending 28 military planes close to the island in June, the largest exercise this year. Japan has demonstrated support for Taiwan, including by donating about two million doses of vaccine to its neighbor, as Taipei has blamed China for impeding shipments of the shots.

While Japan’s pacifist constitution limits the scope of its military, a 2015 reinterpretation of the document allows it to send troops to overseas conflicts in some circumstances.

Aso, 80 and a former prime minister, has a history of controversial remarks, including in 2013 suggesting that Japan learn from the Nazis. He later withdrew the comment. In the early months of the pandemic, he explained Japan’s relatively low death rate from the disease by saying its people were of a different cultural level.

Taro Aso says an invasion of Taiwan by China could be seen as an existential threat, allowing Japan to exercise the right to collective self-defense.

Japan's Deputy PM Taro Aso underlines need to defend Taiwan jointly with US