US President-elect Donald Trump has selected retired Marine Corps general John Kelly to head the Department of Homeland Security.

He also chose Oklahoma Attorney General Scott Pruitt, whose policies have helped fossil fuel companies, to run the Environmental Protection Agency.

Separately, Trump named the former chief executive of World Wrestling Entertainment (WWE), Linda McMahon, 68, to head the Small Business Administration. Trump has taken part in WWE events in the past and has close ties to the McMahons. He also is a member of the WWE Hall of Fame.

Trump also picked up the Time magazine "Person of the Year" distinction, it was announced Wednesday.

Trump's long presidential campaign was in large part defined by searing rhetoric and his steadfast promises to build an impenetrable wall on the border with Mexico and crack down on immigrants living in the United States illegally. But he struck a softer tone in the interview published in Time for the annual feature.

"We're going to work something out that's going to make people happy and proud," Trump said. "They got brought here at a very young age; they've worked here, they've gone to school here. Some were good students. Some have wonderful jobs. And they're in never-never land because they don't know what's going to happen."

Chicago Mayor Rahm Emmanuel presented Trump a letter on Wednesday from 14 big-city mayors urging him to keep the program intact.

"They were working hard toward the American dream," Emmanuel told reporters in the lobby of Trump's skyscraper. "It's no fault of their own their parents came here. They are something we should hold up and embrace."

Trump moved toward making another addition to the collection of generals in his Cabinet, settling on Kelly, 66, to head Homeland Security, according to people close to the transition.

Trump has already picked retired Marine Corps general James Mattis for secretary of defense and retired Army lieutenant general Michael Flynn as national security adviser.

Kelly, who joined the Marines Corps in 1970, retired this year after a final command that included oversight of the Guantanamo Bay detention center.

He has a reputation as a border hawk after a time in the Southern Command, which is based in South Florida and regularly works with Homeland Security on missions to identify and dismantle immigrant smuggling networks.

Trump also picked Pruitt, a longtime critic of the EPA, to head the agency, according to a person close to Pruitt who was not authorized to speak publicly about the choice before it was announced.

The move came just after Trump met with former vice-president Al Gore, who is an environmental activist, and said he had "an open mind" about honoring the Paris climate accords.

"Mr. Pruitt's record is not only that of being a climate change denier, but also someone who has worked closely with the fossil fuel industry to make this country more dependent, not less, on fossil fuels," said Vermont Senator Bernie Sanders.

Oklahoma Senator Jim Inhofe said Pruitt "has proven that being a good steward of the environment does not mean burdening taxpayers and businesses with red tape".

House of Representatives Democratic leader Nancy Pelosi said "the head of the EPA cannot be a stenographer for the lobbyists of polluters and Big Oil."

Trump's campaign manager, Kellyanne Conway, brushed off the criticism, praising Pruitt's record and telling reporters at Trump Tower: "We're very accustomed to the naysayers and the critics."

Also Wednesday, Trump said he planned to name his secretary of state next week and insisted that former rival Mitt Romney still had a chance. Trump, who has met twice with the 2012 GOP nominee, denied he was stringing Romney along to make him pay for saying the former reality show star was unfit to be president.

"No, it's not about revenge. It's about what's good for the country, and I'm able to put this stuff behind us — and I hit him very hard also," Trump said in a telephone interview on NBC.

Those close to the selection process have said that Trump has begun moving away from both Romney and another former front-runner, former New York City mayor Rudy Giuliani.

Senate Foreign Relations Chairman Bob Corker and former CIA director David Petraeus also had been previously identified by transition aides as part of the final four, though Trump has now expanded the pool.