Interior Secretary Ryan Zinke, who is facing federal investigations into his travel, political activity and potential conflicts of interest, will leave the administration at year's end, President Donald Trump said Saturday.

Trump, in tweeting Zinke's departure, said the former Montana congressman "accomplished much during his tenure" and that a replacement would be announced next week. The Cabinet post requires Senate confirmation.

Zinke is leaving weeks before Democrats take control of the House, a shift in power that promised to intensify probes into his conduct. His departure comes amid a staff shake-up as Trump heads into his third year in office. The president on Friday named White House budget director Mick Mulvaney as his next chief of staff

Zinke, 57, played a leading part in Trump's efforts to roll back environmental regulations and promote domestic energy development. When he recently traveling to survey damage from California's wildfires, Zinke echoed Trump claims that lax forest management was to blame in the devastation.

He pushed to develop oil, natural gas and coal beneath public lands in line with the administration's business-friendly aims. But Zinke has been dogged by ethics probes, including one centered on a Montana land deal involving a foundation he created and the chairman of an energy services company that does business with the Interior Department.

Investigators also are reviewing Zinke's decision to block two tribes from opening a casino in Connecticut and his redrawing of boundaries to shrink a Utah national monument.

Zinke has denied wrongdoing.

The Associated Press reported last month that the department's internal watchdog had referred an investigation of Zinke to the Justice Department.

Trump told reporters this fall he was evaluating Zinke's future in the administration in light of the allegations.

Asked by reporters last month whether he might fire Zinke, Trump said, "No, I'm going to look into any complaints."

Zinke in November denied he already was hunting for his next job.

"I enjoy working for the president," he told a Montana radio station. "Now, If you do your job, he supports you."

"I think I'm probably going to be the commander of space command," Zinke said. "How's that one?"

Zinke had a memorable administration debut when he rode a bay roan gelding to his first day of work in March 2017.