Interior Secretary Ryan Zinke faces a Justice Department investigation into whether he used his office for personal gain, following a referral from his agency's own inspector general.

CNN reported on Tuesday it heard from multiple sources that the inspector general referred Zinke to the Justice Department for investigation.

But the exact nature of the DOJ inquiry into Zinke's alleged activities is not clear. Zinke has faced multiple ethics probes, including one involving a real estate deal between Halliburton Chairman David Lesar and a Montana foundation Zinke used to run before giving over leadership to his wife.

Lesar and others involved in the deal met with Zinke at his Interior headquarters in August.

The agency made headlines earlier this months over reports that Zinke looked to replace Interior's inspector general with a Trump administration political appointee.

Zinke told CNN that he has not been contacted by the Justice Department.

"They haven't talked to me," he said. "It will be the same thing as all the other investigations. I follow all rules, procedures, regulations and most importantly the law. This is another politically driven investigation that has no merit."

The Justice Department is not commenting on its investigation into the secretary. The Washington Post also reported that Interior's inspector general referred Zinke to the DOJ.

Zinke is expected to step down after the midterm elections, along with other Cabinet heads, according to reports from Politico and other outlets.