WASHINGTON (Reuters) - U.S. Interior Secretary Ryan Zinke, who has aggressively sought to roll back Obama-era environmental protections, will be leaving his post at the end of the year, President Donald Trump tweeted on Saturday, the latest high-profile departure from his administration.

Trump did not give a reason for Zinke’s departure. However, the former Navy Seal and ex-congressman from Montana has faced scrutiny of his use of security details, chartered flights and a real estate deal.

“Ryan has accomplished much during his tenure and I want to thank him for his service to our Nation,” Trump said on Twitter. “The Trump administration will be announcing the new secretary of the Interior next week.”

Zinke has run the Interior Department, which oversees America’s vast public lands, since early 2017. He has aggressively pursued Trump’s agenda to promote oil drilling and coal mining by expanding federal leasing, cutting royalty rates, and easing land protections despite environmental protests.

Zinke, 51, was among Trump’s most active Cabinet members, cutting huge wilderness national monuments in Utah to a fraction of their size and proposing offshore oil drilling in the Arctic, Pacific and Atlantic. He became a darling of the U.S. energy and mining industries and a prime target for conservationists and environmental groups.

Senate Democratic leader Chuck Schumer welcomed Zinke’s departure in a tweet: “Ryan Zinke was one of the most toxic members of the cabinet in the way he treated our environment, our precious public lands, and the way he treated the govt like it was his personal honey pot.”

“The swamp cabinet will be a little less foul without him,” Schumer said.

Jamie Williams, president of the non-profit Wilderness Society, said he expects Zinke’s deputy and likely successor, David Bernhardt, to continue with the “drill everywhere” agenda.

“Deputy Secretary Bernhardt has made it his mission to stifle climate science and silence the public so polluters can profit,” said Williams. “Unfortunately, even with Secretary Zinke out, the Interior Department remains disturbingly biased in favor of special interests over the health of American communities and the public lands that they love.”

Critics have questioned Zinke’s ethics and some of his moves triggered government investigations.

In July, the Interior Department’s Office of Inspector General began investigating a Montana land deal between a foundation Zinke set up and a development group backed by the chairman of oil service company Halliburton Co, which has business with the Interior Department.

In late October, that investigation was referred to the U.S. Justice Department for a possible criminal investigation, according to multiple media reports. The Department of Justice and the Interior Department have declined to comment.

There are two other investigations of Zinke’s conduct. Interior’s watchdog is examining whether the department purposely redrew the boundaries of Utah’s Grand Staircase-Escalante National Monument to benefit a state lawmaker who owns adjoining property.

US Secretary of the Interior Ryan Zinke arrives at the US Capitol prior to the service for former President George H. W. Bush in Washington, DC, USA, 03 December 2018. Shawn Thew/Pool via REUTERS

It is also probing Zinke’s decision to block casinos proposed by two Connecticut Native American tribes. Critics allege he made that move, overruling his staff’s recommendation, shortly after he met with lobbyists for MGM Resorts International, which owns a new casino in the region.

Zinke has repeatedly denied any wrongdoing.

Earlier this year, Interior’s inspector general wrapped up two other investigations related to Zinke’s travel expenses. Those probes found that a $12,000 private flight he took after a meeting with a professional hockey team could have been avoided and that the security detail he took on a family vacation to Greece and Turkey cost taxpayers $25,000.

Trump, who has repeatedly praised Zinke, said on Nov. 5 that he would look at the allegations.

Zinke’s departure makes him the ninth Cabinet-level official to leave since Trump took office two years ago. Other departures have included Attorney General Jeff Sessions and Environmental Protection Agency chief Scott Pruitt.