BEIJING (Reuters) - China’s difficulties in bringing home graft suspects who fled abroad have prompted tighter measures against illegal moves of capital and people beyond its borders, the government said on Friday.

China has sought to build international cooperation in its hunts for corrupt officials overseas, after President Xi Jinping launched a war on graft about four years ago.

But some Western nations have been reluctant to send people back to a country where rights groups say mistreatment of criminal suspects remains a problem, and they also say China is unwilling to furnish proof of the crimes.

The People’s Bank of China and the Public Security Ministry have cracked down on the use of offshore companies and underground transfers of capital this year, the Central Commission for Discipline Inspection (CCDI) said.

“Preventing one person from fleeing abroad is to a certain degree the same as recovering one, so we must unceasingly increase efforts to prevent escape,” said Liu Jianchao, head of the graft agency’s international cooperation bureau.

At the same time as weaving a web overseas, ‘Sky Net’ must build a dam to keep individuals from moving overseas, the agency said on its website.

It was referring to a program dating from 2014 that has drawn on the resources of several Chinese agencies to track and repatriate corrupt officials and their plunder.

Fewer suspects left China in 2016 than last year, when returning suspects for the first time exceeded those who left, the agency said, but gave no figures.

Bringing home the plunder was “very difficult,” Huang Shuxian, deputy head of the agency, said in April.

The operation has recovered 2.3 billion yuan ($333 million) in the first eleven months of this year, or less than a third of total recoveries of 85.4 billion yuan ($12.4 billion) since 2014, the agency said.

China tracks capital outflows closely and regularly steps up measures to restrain abnormal flows. Last month, the central bank vowed to tighten checks against money laundering in Shanghai’s free trade zone.

The anti-graft body also joined hands with three ministries this year to stamp out use of illegal documents during emigration, it added.