China's top anti-graft watchdog said on Friday that it had carried out inspections at six major state-owned enterprises in industries ranging from energy to construction, as the Communist Party of China expands its anti-corruption dragnet.

Energy giant China Huaneng Group, steel producers Baosteel and Wuhan Iron and Steel, China State Construction, China Shipbuilding Industry Corp, and China Ocean Shipping Co were the latest enterprises to be investigated by the Central Commission for Discipline Inspection, the agency said.

The watchdog did not name any executives as targets for individual inspection in its statement, but said it warned companies against transgressions such as nepotism, wasteful spending and improper bidding on contracts.

As part of President Xi Jinping's two-year, multiphase crackdown on corruption, the commission has pledged to inspect "all important backbone State-owned firms and financial institutions" this year.

The watchdog investigated more than 70 senior officials at state firms last year and has carried out inspections in the energy, telecom and financial sectors. A total of 26 firms will be inspected this year, the commission said.