WASHINGTON (Reuters) - The U.S. Interior Department’s watchdog said in a letter to lawmakers on Wednesday that it was investigating a Montana real estate deal involving a foundation set up by Interior Secretary Ryan Zinke and a development group backed by the chairman of oil service company Halliburton.

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

The letter, a copy of which was seen by Reuters, said that the agency’s 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.

Neither the inspector general’s office nor the Interior Department, which comments on behalf of Zinke, replied to requests for comment.

Halliburton spokeswoman Emily Mir said in an email that Lesar’s “personal investment in a small land development in Montana has nothing to do with Halliburton, and the company is confident that any actions of the Interior Department will not be influenced by (his) personal investment.”

The deal, reported by Politico in June, included a hotel, retail shops and microbrewery.

The brewery would be set aside for Zinke and his wife Lola to own and operate, Whitefish city planner said in the Politico story, though the developer said at the time that no final decision had been made.

Politico reported that Zinke’s foundation, the Great Northern Veterans Peace Park Foundation, had pledged in writing to allow the Lesar-backed developer to build a parking lot for its Peace Park project.

Zinke’s wife Lola is president of the foundation, a position she took over from her husband when he became secretary.

The letter, first reported by Politico, was addressed to U.S. Representatives Raul Grijalva, Donald McEachin and Jared Huffman, all Democrats, who had asked the inspector general to investigate if Zinke had used taxpayer resources to advance land developments.

The letter said the investigation had been opened because the lawmakers “expressed special concern about the reported funding by a top executive at Halliburton and assuring decisions that affect the nation’s welfare are not compromised by individual self-enrichment.”

Zinke has pushed for opening federal lands for energy development as the Trump administration pursues a policy of energy dominance to maximize production of crude, natural gas and coal.

The Interior Department’s inspector general has also been investigating Zinke over travel issues since late last year after reports that he had used a private plane owned by an oil executive while secretary.