China National Petroleum Corp. said it was undergoing an internal probe after an audit uncovered widespread corruption.

Chinese President Xi Jinping vowed to crack down on official corruption, which has been publicly recognized by his administration as a threat to the country's overall security.

CNPC said Thursday it would work to clear "private coffers" among its subsidiaries with the aim of addressing embezzlement and general corruption.

As much as $98 million was redirected to staff at CNPC and its subsidiaries, including PetroChina, the National Audit Office found.

CNPC said its subsidiaries are tasked with vetting its leadership and issuing detailed reports on corruption among their ranks.

Four executives at PetroChina were dismissed last year for "serious violations" of corporate principles. Rumors circulated in mid 2013 that PetroChina would be split up because of a corruption scandal.