BEIJING (REUTERS) - No part of China's ruling Communist Party is off limits for its crackdown on corruption, the country's top graft buster was quoted as saying, sounding a warning a few days after one of the country's most senior former soldiers was purged.

Speaking during a visit to the northern region of Inner Mongolia, Wang Qishan, who heads the party's efforts to combat corruption, warned that every part of the party would be liable for inspection.

"Inspection work is a 'health check' for the party. There are no off limits for oversight within in the party, and there are no exceptions," the party's graft watchdog cited Wang as saying in a statement issued late on Friday.

President Xi Jinping, who heads the Central Military Commission (CMC) which controls the 2.3 million-strong armed forces, has launched a drive against pervasive graft since assuming office. He has vowed to take down powerful "tigers" as well as lowly "flies".

The party this week announced that Xu Caihou, who retired as vice-chairman of CMC last year, had been expelled from the party and will be court-martialled after being accused of corruption.

Xu is the most senior person to date to have been felled. However, a potentially far bigger scandal is brewing - the case of the powerful former domestic security chief, Zhou Yongkang.

Sources have told Reuters that Zhou is under virtual house arrest, and while the party made no announcement about his case, many of his allies have been publicly taken down.

On the same day Xu's fate was announced, three other former senior officials were also expelled from the party, all closely connected with Zhou, including the one-time head of the state assets regulator and a former deputy public security minister.

The party has sent numerous teams into the provinces and government departments to expose corruption. Problems discovered during this process show that the party is "absolutely correct" in its judgement that corruption remains a serious and complex problem, Wang added.

"It warns us that we must take the arresting of the spread of corruption as our aim and mission, and that these inspections are absolutely something we cannot do without," he said.