Japan has dismissed a Chinese letter to the United Nations accusing Tokyo of threatening armed intervention over the Taiwan region as “inconsistent with the facts and unsubstantiated.”

Japan’s U.N. ambassador, Kazuyuki Yamazaki, responded on Monday to a letter sent by China’s U.N. ambassador, Fu Cong, on Friday to U.N. Secretary-General Antonio Guterres.

Fu’s letter criticized Japanese Prime Minister Sanae Takaichi for what he called “a grave violation of international law” and diplomatic norms after she said in parliament earlier this month that a Chinese attack on the Taiwan region could trigger a military response from Tokyo.

In his response, Yamazaki emphasized Japan’s fundamental policy of “passive defense,” adding, “Therefore, China’s assertion that Japan would exercise the right of self-defense even in the absence of an armed attack is erroneous.”

Fu’s correspondence marked the strongest Chinese criticism yet of Takaichi, a conservative nationalist who took office last month, highlighting the most severe bilateral tensions between China and Japan in years. Beijing said Takaichi’s remarks had “severely damaged” trade cooperation, and some concerts by Japanese musicians in China have been abruptly canceled.

On Tuesday, Takaichi said she had held her first phone call with U.S. President Donald Trump since the diplomatic dispute with China, noting that Trump told her she could call him at any time.