Prosecutors in Shanghai have indicted Peter Humphrey, a 58-year-old UK citizen, and Yu Yingzeng, a 61-year-old US citizen, for illegally obtaining personal information on Chinese citizens, the official Chinese news agency Xinhua reports.

It is the first indictment Chinese prosecutors have announced of foreigners for conducting an illegal investigation, according to Xinhua.

The agency said local courts will hear the case of the two investigators at an unspecified date.

The couple, which registered their company, ChinaWhys, in 2004 in Shanghai, is accused of having illegally bought or obtained information through secret photography and infiltration.

According to Western news agencies, the company had previously been hired by Glaxo, which is under a bribery investigation in China.

China last year began an investigation into Glaxo's sales practices in the country, detaining some of its employees there.

On July 3, the drugmaker said ChinaWhys was hired last year to investigate a breach of privacy and security related to its China general manager.

The news agency Bloomberg said the office and mobile phone numbers for ChinaWhys' Shanghai headquarters appear to have been disconnected, and emails to the corporate account listed on the site were not answered.