China will investigate all major state-owned enterprises (SOEs) this year, a Communist Party watchdog announced Wednesday, in the latest step of President Xi Jinping's much-publicised anti-graft campaign.

The move is likely to send tremors through the ranks of China's state firms, which command immense power over large sectors of the country's economy.

The Central Commission for Discipline Inspection (CCDI), the ruling Communist Party's much-feared internal investigative organ, announced the move in a communique at the conclusion of its fifth plenum.

"This year, we will strengthen supervision of state-owned enterprises," the group said in its communique, which was posted on the CCDI website.

The anti-graft campaign has netted high-level "tigers" as well as low-level "flies", but critics say that it risks being influenced by politics without systemic reforms to prevent corruption such as public disclosure of assets and an independent judiciary.

The powerful targets to have fallen since Xi came to power include former internal security chief Zhou Yongkang and Ling Jihua, a onetime aide to former President Hu Jintao.

In its communique, the CCDI also issued a stern warning against cadres forming factions, echoing Xi's words on the subject in a recent speech.

"Our party will absolutely not tolerate cliques or factionalism," the communique states. "We will not allow members to go their own way or feign compliance."

Last month, the CCDI announced that for the first time ever, it would send investigators to the country's parliament, the National People's Congress, in a demonstration of the party's dominance over the organs of state.

The crackdown on corruption and extravagance has increasingly targeted the powerful state sector, which has been enriched by close ties to the government and lack of competition.

In August, China's top leaders decided to cut salaries and restrict expense accounts and other perks of SOE executives.