WASHINGTON, D.C. — The Interior Department’s top watchdog has referred an investigation into Secretary Ryan Zinke to the Justice Department, raising the prospect that criminal violations have been uncovered, The Washington Post reported on Tuesday.

The Interior Department’s inspector general has been looking into several inquiries involving Zinke, including accusations over his wife’s travel and a land deal with a property development group backed by the chairman of the oilfield services company Halliburton Co. The Post cited anonymous sources and did not say which investigation had been referred to the Justice Department.

Representatives of the inspector general’s office and the Interior and Justice departments did not immediately respond to requests for comment.

Zinke’s lawyer, Steve Ryan, said the secretary “has not been contacted or notified of any DOJ 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,” Ryan said by email. “The secretary has done nothing wrong.”

Zinke, a former Navy SEAL and a congressman from Montana, has drawn controversy throughout his two-year tenure at the Interior Department, which oversees parks, oil drilling and other activities on about 500 million acres of U.S. lands.

Critics have raised questions about his ethics, as well as his policy decisions, including recommendations to shrink national monuments and moves to encourage oil development.

The Interior Department’s inspector general has been reviewing Zinke’s involvement in the land deal with a development group backed by Halliburton Co.’s David J. Lesar.

The inspector general recently concluded that Zinke broke department policy by allowing his wife, Lolita, to travel with him in government vehicles and said Zinke could have taken steps to avoid spending $12,375 on a charter flight last year.

In all, Zinke has faced or is facing 15 inquiries, making him the most investigated interior secretary in recent times, according to the Center for Western Priorities, a watchdog.

“Since stepping into his role as interior secretary, Ryan Zinke has repeatedly leveraged his office for personal gain, attracting unprecedented scrutiny from government investigators,” said Jennifer Rokala, executive director of the Denver-based group.

Rep. Raul Grijalva, an Arizona Democrat who stands to lead the congressional committee charged with overseeing the Interior Department if Democrats take control of the House, vowed to grill Zinke.

“Secretary Zinke will be called to testify in February on why his conduct in office merited referral to the Justice Department,” Grijalva said. “The critical work of the Interior Department in combating climate change, protecting our special places and saving endangered species cannot get done until we clean up the ethical mess plaguing the department, and it’s clear House Republicans won’t do it,” he added.