WASHINGTON -- US President Donald Trump said Saturday that Interior Secretary Ryan Zinke will step down at the end of this year.

"Secretary of the Interior @RyanZinke will be leaving the Administration at the end of the year after having served for a period of almost two years," the president tweeted.

In a follow-up tweet, Trump added that his administration will announce a new secretary of the interior next week.

The president did not give a reason for Zinke's departure, but the official, a champion of Trump's environment policy, has been engulfed by several investigations involving alleged managerial misconduct and conflicts of interest.

The most serious of the allegations, according to US media reports, focuses on whether Zinke used his power as interior secretary to gain personal profit in a land deal in his hometown of Whitefish, Montana.