A knife attack at a restaurant in China’s financial hub Shanghai has left three people injured, including two Japanese nationals, the Chinese foreign ministry said Wednesday, describing the incident as isolated.

Foreign ministry spokesperson Guo Jiakun said Chinese authorities are investigating the Tuesday attack and that the suspect has been detained. He added that the accused is believed to have a mental disorder.

Along with the two Japanese citizens, a Chinese national was also injured in the attack and all three were taken to hospital for treatment.

Guo urged media and the public not to speculate about the incident or draw unverified conclusions.

The attack comes at a time of strained relations between China and Japan.

Tensions between the two countries have increased since Japanese Prime Minister Sanae Takaichi said in November that any Chinese military action against Taiwan could prompt a Japanese response. Beijing later imposed diplomatic and economic measures against Tokyo.

In April, the Chinese Embassy in Japan also said it had received threats and accused Japanese authorities of not taking sufficient action despite repeated complaints to police.

Chinese officials, however, stressed that the Shanghai stabbing should not be linked to broader political tensions between the two countries.