WASHINGTON — Secretary of the Interior Ryan Zinke will step down at the end of the year, amid a series of investigations that include conflict of interest.

“Secretary of the Interior Ryan Zinke will be leaving the Administration at the end of the year after having served for a period of almost two years. Ryan has accomplished much during his tenure and I want to thank him for his service to our Nation,” Trump tweeted Saturday. “The Trump Administration will be announcing the new Secretary of the Interior next week.”

A week ago, Trump announced that Chief of Staff John Kelly would be departing at year’s end. Mick Mulvaney, who has been the White House director of the Office of Management and Budget, will serve as acting chief of staff.

Zinke’s tenure has been marked by ethics inquiries and his involvement in a land deal in Montana that is backed by the chairman of Halliburton. The company has an interest in Department of Interior decisions on whether to open public lands for drilling. Zinke’s use of public funds for travel also has come under scrutiny.

He’s also drawn opposition from environmental groups, particularly for proposals to reduce the size of national monuments.

Zinke was a congressman from Montana from 2015 to 2017.