"Recent articles about official Interior Department helicopter usage are total fabrications and a wild departure of reality," he said in a statement posted with the tweet. "On these instances, I conducted an aerial survey of a million acres of federal monument lands, an aerial survey of a power line project which was under scrutiny for possible compensatory migration corruption from the previous administration, and a national command authority directed emergency response exercise."
"All of these instances were thoroughly vetted and scrutinized before being approved by the Department's career ethics officers and solicitors," he said.
Zinke's use of Interior Department and other helicopters was revealed earlier this year when the department released his office and travel schedules in response to Freedom of Information Act requests. Documents show that helicopter trips to and from events within a few hours of his Washington office cost taxpayers more than $14,000. He provided no proof of inaccuracies in his statement.
Sen. Maria Cantwell, a Democrat from Washington state, called for the investigation to include Zinke's "taxpayer-funded helicopter rides."
"If he misused public funds, he should write the Treasury a check for the full amount & apologize," she said.
The Interior Department Inspector General's Office declined to say Friday whether its investigation, which began earlier this year after Zinke's trips to the US Virgin Islands and Las Vegas combined work with political events, includes the helicopter use.
"We are taking a comprehensive look at the secretary's travel since he took office," said Nancy DiPaolo, the inspector general's spokeswoman.
Interior spokeswoman Heather Swift said one flight was necessary for Zinke to attend "an official congressional event" -- the swearing-in of his successor, Montana Republican Greg Gianforte, to the US House -- "before going to an emergency management briefing."
Travel records show Zinke used government and state-owned helicopters on other occasions, such as when touring national monuments during his review of federally owned land.