WASHINGTON — The Interior Department’s internal watchdog has referred an investigation of Secretary Ryan Zinke to the Justice Department, signaling a potential escalation amid a series of inquiries into Zinke’s conduct.

Two people familiar with the investigation said Interior’s office of inspector general referred a case involving Zinke to Justice. It is not clear what the investigation is focused on.

Zinke faces a number of probes, including one centered on a Whitefish land deal involving a foundation he created and the chairman of Halliburton, a prominent energy services company that does significant business with Interior.

Investigators also are reviewing Zinke’s decision to block two tribes from opening a casino in Connecticut and his redrawing of boundaries to shrink a Utah national monument.

Zinke has denied wrongdoing, and his lawyer said Zinke has not been notified of any Justice Department investigation or inspector general referral.

“It is disappointing that unsubstantiated and anonymous sources have described an IG office referral to members of the media, as this violates DOJ and IG policy direction. The secretary has done nothing wrong,” lawyer Steve Ryan said in an emailed statement.

Nancy DiPaolo, a spokeswoman for Deputy Inspector General Mary Kendall, said she cannot comment on ongoing investigations.

Spokeswoman Nicole Navas Oxman said Justice “generally does not confirm, deny or otherwise comment on the existence or non-existence of an investigation.”

The referral was first reported by The Washington Post.

Arizona Rep. Raul Grijalva, the top Democrat on the House Natural Resources Committee, said if Democrats win a House majority next week, Zinke will be called to testify “on why his conduct in office merited referral to the Justice Department, whether that referral was related to the recent attempted firing of his inspector general, and his many other failures and scandals.”

Grijalva was referring to a short-lived bid by the Trump administration to reassign a political appointee at the Department of Housing and Urban Development to replace Kendall as acting head of the inspector general’s office.

HUD Secretary Ben Carson said in an Oct. 12 email that then-assistant HUD secretary Suzanne Israel Tufts would take over the watchdog role. Tufts ultimately was not tapped for Interior and resigned from the administration.

Grijalva and other Democratic lawmakers called for an investigation this summer after reports that a charitable foundation created by Zinke and run by his wife, Lola, was allowing a company co-owned by Halliburton chairman David Lesar to use the foundation’s land for a commercial development.

Zinke also met Lesar, Lesar’s son and Whitefish developer Casey Malmquist in his Washington office last year, according to emails the Democrats received in a public records request.

Lesar is a financial investor in 95 Karrow LLC, the company with plans to redevelop the former Idaho Timber mill site off West Second Street in Whitefish. The project involves a shared-use agreement between 95 Karrow and the Great Northern Veterans Peace Park Foundation for a parking lot to be built on the private park land known as the Great Northern Veterans Peace Park.

Zinke, though his foundation, expressed plans for a public sledding hill, but the park property remains undeveloped.

Zinke has come under scrutiny for his travel practices and other actions as secretary. He has dismissed the allegations as politically motivated.

The inspector general’s office said in a report last month that Lola Zinke was allowed to ride in government vehicles with him despite a department policy that prohibits nongovernment officials from doing so. The report also said Interior spent more than $25,000 to provide security for the couple when they took a vacation to Turkey and Greece.

Interior spokeswoman Heather Swift said the report shows Zinke “follows all relevant laws and regulations” and that his travel was reviewed and approved by career ethics officials and department lawyers.

The Whitefish Pilot contributed to this story.