Chinese prosecutors have indicted a Japanese citizen on suspicion of espionage, China's foreign ministry said on Thursday, adding that the rights of the people involved in the case would be protected.

The individual was indicted recently in line with the law, Mao Ning, a spokesperson at the ministry, said at a regular press conference when asked about the indictment of a Japanese employee of Astellas Pharma.

Ties between China and Japan have grown tense in recent years as they contend with issues from territorial claims to Tokyo's decision to release treated water from the crippled Fukushima No. 1 nuclear plant into the sea.

Arrests of Japanese citizens in China have fueled those tensions.

The detention of the Astellas employee in China last year has cast a chilling effect on business, some Japanese officials have said, contributing to a drop in foreign investment and an exodus of Japanese expatriates.

The Japanese pharmaceutical company said on Wednesday that one of its Japanese employees detained since March 2023 on suspicion of spying had been indicted by Chinese authorities, without naming the individual.

Japan's foreign ministry said a man in his 50s detained in Beijing last year was indicted in mid-August, also without identifying the person.

"China is a country with the rule of law, that investigates and deals with law-breaking and illegal activities in accordance with the law," Mao said.

"At the same time (China) safeguards the legitimate rights and interests of the people involved, and facilitates the duties of Japanese consular officials stationed in China," she said.