BEIJING (REUTERS) - Three people on China's list of 100 most wanted graft suspects overseas were not prosecuted when they finally returned to China, the government has said in an update on the cases of 40 people on the list it has had returned.

China has pursued an overseas search, dubbed Operation Fox Hunt, for corrupt officials and business executives who have fled abroad with their assets, part of President Xi Jinping's war on deep-seated corruption.

In 2015, the authorities published a list of 100 of the most wanted corruption suspects who had been targeted with an Interpol red notice, many living in the United States, Canada and Australia.

An update released by the graft-busting Central Commission for Discipline Inspection late on Wednesday (May 10) said 15 of the 40 returnees had already been sentenced to terms of up to life in prison.

Some came back voluntarily, while others were extradited.

However, three people were let off after returning to China.

The commission said Zhang Dawei was exempted from prosecution in November 2016 because he had confessed his crime and returned all his illegal gains voluntarily.

Two others, Zhu Zhenyu and Zhang Liping, were spared prosecution because Zhu was an accessory to the crime and turned himself in voluntarily, while Zhang's offence of falsifying value-added tax invoices was judged too minor, it said.

The handling of these cases reflects China's policy of offering leniency to those who voluntarily return while giving harsh penalties for those who are brought to justice after being arrested, the commission said.

The case of the person who topped the list of 100, Yang Xiuzhu, was listed among a group of 13 people described as having their cases still under investigation or awaiting review.

Yang, a former deputy director of the construction bureau in the south-eastern city of Wenzhou, ended 13 years on the run by returning from the United States last November.

China has been trying to drum up international cooperation in its hunt for suspected corrupt officials who have fled overseas since Mr Xi began his war on graft more than four years ago.

Many Western countries, however, have been reluctant to help, or to sign extradition treaties, unwilling to send people back to a country where rights groups say mistreatment of criminal suspects remains a problem.

They also complain China is often unwilling to provide proof of the crimes.