BEIJING (Reuters) - Fixing the corruption problem in China’s ruling Communist Party is “world class hard” and the battle will never end, the country’s top graft-buster told Singapore’s prime minister in a rare meeting with a visiting foreign leader.

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Wang Qishan, who heads the party’s Central Commission for Discipline Inspection, has been at the forefront of President Xi Jinping’s fight against deep-seated corruption, and speculation has swirled about whether he will retire or stay on at next month’s key party Congress.

Meeting Singapore Prime Minister Lee Hsien Loong at the central leadership’s Zhongnanhai compound in Beijing, Wang said the party’s anti-corruption campaign and efforts to supervise itself had been highly effective.

“Carrying out an operation on yourself to cure an illness is world class hard,” the commission cited Wang as saying, in a statement late on Wednesday.

The party has long insisted it has no need for an independent anti-corruption mechanism, in a country where the party also controls the legal system.

Wang said that the final aim in the graft fight was to find an effective route to self-supervision for a party that has been in power for a long time, and to always maintain the party’s “progressiveness and cleanliness”.

The party’s efforts have won the trust of the people and demonstrates the party’s confidence in its system, he added.

The anti-corruption effort is “always on the road”, Wang said, using a frequently used party expression to refer to how the campaign will not end.

Singapore’s Straits Times said that the meeting with Wang had been requested by Lee, and that Wang told Lee he was surprised but happy the request had been made.

“So I sought permission and I am here meeting you and your delegation today,” Wang told Lee, the newspaper reported.

Wang, who is 69 and sits on the party’s elite ruling Standing Committee, should retire at next month’s party Congress according to unwritten party rules on age limits, but he is close to Xi and could stay on in some capacity, sources with ties to the leadership have said.