Interior Department Secretary Ryan Zinke is said to be under investigation by the Department of Justice (DOJ).

The Washington Post and other outlets reported Tuesday that Interior's Office of Inspector General (IG) had referred an ongoing probe to the DOJ, citing two individuals familiar with the matter. CNN later reported that the DOJ was looking into whether Zinke was using his office for personal gain, but the full extent of the investigation was unclear.

Zinke told CNN that he had not been contacted by the DOJ. "It will be the same thing as all the other investigations," he told the network. "I follow all rules, procedures, regulations and most importantly the law. This is another politically driven investigation that has no merit."

The IG opened an investigation into Zinke last July. The IG informed Reps. Raúl Grijalva (D-AZ), Donald McEachin (D-VA) and Jared Huffman (D-CA) that it launched the probe into allegations that Zinke violated conflict of interest laws by cooperating with a Halliburton Co. executive to advance land developments in Zinke's hometown, Whitefish, MT.

CNN also reported that the IG is looking into whether the Trump administration's decision last December to reduce the Grand Staircase-Escalante National Monument in southern Utah from 1.88 million acres to about 1 million acres was done to benefit a local politician. Zinke reportedly backed the reduction.

"Referring Zinke to the DOJ for his conduct in office is yet another reason to fire him," Friends of the Earth spokeswoman Nicole Ghio said Tuesday. "If the IG believes Zinke broke the law, the secretary must be removed from office as quickly as possible. Zinke has shown time and time again that he will put himself and his political donors before the good of this country."