U.S. President Donald Trump said on Monday he will nominate David Bernhardt, a former energy lobbyist, to be secretary of the interior, the department that oversees the country's public lands.

Bernhardt is currently the acting secretary at the Interior Department. He is widely expected to continue pushing the Trump administration's plan to boost domestic fossil fuels production, by opening more U.S. public lands to drilling and mining.

"David has done a fantastic job from the day he arrived, and we look forward to having his nomination officially confirmed," Trump said on Twitter.

Bernhardt would replace Ryan Zinke, who was under a cloud of ethics investigations and announced his resignation in December.

The Interior Department, which employs more than 70,000 people and oversees more than 20 per cent of the U.S. land surface, has played a large role in Trump's "energy dominance" policy of boosting energy production.

As Zinke's deputy, Bernhardt was part of efforts to open Alaska's Arctic National Wildlife Refuge to oil drilling, ease Obama-era protections on a bird called the greater sage grouse to boost drilling and mining across the West, and open federal lands to leases for coal mining. He is likely to be careful to avoid the missteps that plagued Zinke.

Ann Navaro, a former Department of Interior official who served in the Obama and Trump administrations and worked closely with Bernhardt, said he is a rare "lawyer's lawyer" who prepares thoroughly for meetings, often being the only one in a room to have read full environmental assessments of projects and plans.

Bernhardt, who prefers conservative suits to Zinke's cowboy hats and boots, also worked a series of jobs at the Interior Department under former president George W. Bush from 2001 to early 2009, including as the department's solicitor.

After working under Bush, Bernhardt worked as a lawyer and lobbyist at Brownstein Hyatt Farber Schreck, for water and oil interests. He represented Noble Energy Co., Rosemont Copper Co., Sempra Energy, and California's Westlands Water District, among others.

Critics say Bernhardt's previous work as a lobbyist could risk conflicts of interest, unless he recuses himself from certain issues, because he worked for companies that could benefit by opening up lands to development.

His nomination requires Bernhardt to again be confirmed by the U.S. Senate.

In 2017, about 150 environmental groups, including the business-friendly Natural Resources Defense Council, urged senators in a letter to oppose Bernhardt in the confirmation vote for his deputy position, saying his previous lobbyist work raised questions about his ability to act in the public interest.

Despite their letter calling him a "walking conflict of interest," the Senate confirmed Bernhardt on a 53-43 vote, and with strong support from Sen. Lisa Murkowski of Alaska and other lawmakers who have large areas of U.S. lands in their states.