Japan has confirmed Chinese authorities have arrested a third Japanese citizen and detained another on suspicion of spying.

The series of arrests and detentions could strain already tense ties between Asia's two largest economies.

Tokyo's top government spokesman Yoshihide Suga said Friday that a Japanese woman, who had been detained in Shanghai in June, wasformally arrested in November.

He also said a Japanese man has been under criminal detention after being held in Beijing in June.

In September, China said it had arrested two Japanese citizens for suspected spying.

A total of four Japanese are now being held by Chinese authorities on suspicion of espionage.

"Japan does not engage in such (spying) activities in any countries," Suga told reporters, without elaborating.

Japan and China have taken steps over the past year to improve ties but relations remain shaky.

Tokyo is particularly wary as Beijing becomes increasingly aggressive in pressing its various sovereignty claims, including a dispute with Japan over ownership of a group of islands.