Chinese police have detained a man suspected of wounding three people, including two Japanese nationals, in a knife attack on a bus used by a Japanese school in the eastern city of Suzhou, local authorities said on Tuesday.

Police arrested the suspect, an unemployed man in his 50s whose family name is Zhou, on the spot after Monday’s attack, local police said in a statement, adding that he was under investigation.

The wounds of the two Japanese are not life threatening, while the Chinese citizen who was the most critically wounded is still undergoing treatment, the statement added.

An official at the Japanese consulate in Shanghai had told Reuters on Monday that a Japanese woman and her pre-schooler had been waiting for the bus at a stop when they were attacked. A Chinese woman was also wounded.

On Tuesday, China’s foreign ministry spokesperson Mao Ning called the attack an “isolated incident” that could have happened in any country in the world. China has seen a spate of similar knife attacks in recent months.

Last week, a 54-year-old male suspect was arrested after a knife attack that wounded three people inside a subway station in Shanghai.

Two weeks ago, four American instructors from a small Iowa university were wounded in what appeared to be a random stabbing attack in northeastern Jilin province, prompting Beijing to promise it would take measures to ensure the safety of foreigners. A 55-year-old local man was detained the same day.

In May, two people were killed and 21 wounded in a knife attack at a hospital in southwest Yunnan province.