The cases of Zhou Yongkang and Xu Caihou, disgraced former senior officials, demonstrate that some corrupt officials "are very well hidden" within the Communist Party of China (CPC), the Party's graft watchdog cited a bylined commentary on its website on Monday.

According to the commentary quoted by the CPC Central Commission for Discipline Inspection (CCDI), these hidden tigers (high-ranking officials) tend to form cliques and factions, seeking not only money but also political conspiracy, gravely threatening the Party leadership and solidarity.

"The tigers we aim at nowadays are deceitful, and tend to lay low," the article went on, warning that corrupt officials find their ways to survive the sweeping anti-graft campaign.

The commentary argued that the fight against corruption must be carried on, in light of the daunting challenges, refuting opinions that "the anti-graft campaign is just a gust of wind."

"Some call on an end to the combat against graft and work style revamp, fearing the campaign would go too far if it continues," the article said, adding "such arguments must be vehemently objected."

It said, the nerve-wracking hunt after corruption has given some officials sleepless nights, while the people hail downfalls of corrupted officials. The anti-graft campaign must continue as the people anticipate, and keep unnerving undisciplined officials.

Zhou Yongkang, a former member of the Standing Committee of the Political Bureau of the CPC Central Committee, was arrested and expelled from the CPC in December, for serious breaches of the Party's political, organizational and confidentiality rules, as well as suspected crimes.

Xu Caihou is former Central Military Commission vice chairman and by far the highest ranking military official being investigated and prosecuted.