U.S. Interior Secretary Ryan Zinke testifies before a Senate Appropriations Interior, Environment and Related Agencies Subcommittee hearing on the FY2019 funding request and budget justification for the Interior Department, on Capitol Hill in Washington, U.S., May 10, 2018. REUTERS/Yuri Gripas/File Photo

WASHINGTON (Reuters) - The U.S. Interior Department’s acting inspector general has referred a probe into Interior Secretary Ryan Zinke’s conduct to the Justice Department for further investigation, media reports said on Tuesday, citing unnamed sources.

Referring a probe to the Justice Department means it will explore whether evidence warrants a criminal investigation. Mary Kendall, the acting inspector general of the Interior Department, is conducting at least three probes into Zinke’s conduct, but it was not clear which one had been sent to the Justice Department, the Washington Post said.

Among other investigations, Kendall is probing Zinke’s involvement in a Montana land deal and a decision not to grant two tribes approval to run a casino in Connecticut.

A senior White House official said the White House understands the DOJ investigation is looking into whether the secretary “used his office to help himself,” according to the Washington Post.

The Interior Department’s inspector general said in a letter to lawmakers in July that the office was investigating a Montana real estate deal involving a foundation set up by Zinke and a development group backed by the chairman of oil service company Halliburton Co.

The letter said the inspector general had launched the probe on July 16 to look into a development deal in Zinke’s hometown of Whitefish, Montana, between a group funded by David Lesar, Halliburton’s chairman, and the foundation. The deal was first reported by Politico.

A Lesar spokeswoman said in July that his personal investment had nothing to do with Halliburton and that the company was confident the Interior Department would not be influenced by it.

The Interior Department did not immediately respond to a request for comment. Zinke told CNN that he had not been contacted by the Justice Department, that he follows the law, and that the DOJ investigation was “politically driven” and “has no merit.”

Nancy DiPaolo, spokeswoman for the Interior Department’s inspector general office, said she could not comment on any ongoing investigation. The White House and the Department of Justice did not immediately respond to requests for comment.