Refiner CITGO Holding Inc. said it will cooperate in the U.S. Department of Justice's investigation regarding the alleged bribery of U.S. suppliers to its former parent firm Venezuelan state-owned Petróleos de Venezuela SA, according to a June 3 report from Reuters.

The department is seeking records from Citgo for the bribery investigation.

The investigation has already resulted in charges against 21 people, with 16 pleading guilty as of this month.

Citgo told Reuters it has engaged outside counsel to conduct an independent investigation and will take remedial actions in response to the findings.