BEIJING (AP) — A knife attack at a restaurant in Shanghai on Tuesday injured three people, including two Japanese citizens and a Chinese national, the Chinese Foreign Ministry said, calling it an isolated case.

The suspect described as a person with a mental disorder was detained and the victims were taken to a hospital for treatment, Foreign Ministry spokesperson Guo Jiakun said Wednesday.

The two Japanese are men, including a senior employee of a Japanese company with an office in the building where the attack occurred, while the Chinese citizen is a woman, and the Japanese consulate in the city said the injuries of both men are not life-threatening, Japan’s Kyodo News Agency reported.

Japanese Chief Cabinet Secretary Minoru Kihara said Wednesday his government has extended support for the injured men, adding that Japan demanded a thorough investigation and a clear explanation by Chinese officials, severe punishment for the suspect, preventive measures and the protection of Japanese nationals in China.

Japan’s Foreign Ministry issued a safety advisory for Japanese citizens in China to be cautious and attentive, avoid going out alone and take care when accompanying children.

Guo of the Chinese Foreign Ministry said authorities were investigating and media outlets and others should not make “groundless speculation” about the case.

The attack comes at a time of rising tensions between China and Japan.

Ties between Beijing and Tokyo have been strained since Japanese Prime Minister Sanae Takaichi’s comment in November that any Chinese military action against self-ruled Taiwan could be grounds for a Japanese military response. China imposed diplomatic and economic measures against Japan.

The Chinese Embassy in Japan said in April it had received multiple threats and accused Japanese authorities of failing to take effective measures despite repeated reports to the police.

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Associated Press writer Mari Yamaguchi contributed from Tokyo.