BEIJING (Reuters) - The Chinese military needs to be on its guard against corruption rearing its head again, the official People's Liberation Army Daily said on Friday (Aug 25), warning the arrow cannot be put back in the quiver in the fight.

China's military, the world's largest and currently undergoing an ambitious modernisation campaign, has been an important focus of President Xi Jinping campaign against deep-seated graft since he took power almost five years ago.

Dozens of officers have been investigated and jailed, including Xu Caihou and Guo Boxiong, both former vice chairmen of the powerful Central Military Commission, which Xi heads.

Guo was jailed for life last year. Xu died of cancer in 2015 before he could face trial.

In a lengthy front page story, the People's Liberation Army Daily said the "illusions of the corrupt elements had been smashed" and that the "evil begotten" by Xu and Guo had been cleared away like smog dispersed by the wind.

However, the corruption fight needed to continue, not stop, with perseverance and tenacity, the paper said.

"Ice that is three feet thick was not formed overnight; melting three feet thick ice will also not happen overnight," it said, using a classical Chinese aphorism about not being able to accomplish a difficult task easily or quickly.

A hard task remains to ensure the armed forces are clean and that the influence of Guo and Xu are fully purged, the paper added. "It remains a difficult mission to prevent a rebound and a resurgence," it added, saying "the arrow cannot be sheathed once the bow is drawn". "The zero tolerance attitude will not change." Serving and retired officers have said graft in the armed forces is so pervasive it could undermine China's ability to wage war.

The anti-graft drive comes as Xi steps up efforts to modernise forces that are projecting power across the disputed waters of the East and South China Seas, though China has not fought a war in decades.