President-elect Donald Trump sought Thursday to comfort victims of an apparent jihadist-inspired attack in Ohio while under fire for picking a global warming skeptic as his new environment chief.

The 70-year-old property tycoon, who has never previously held elective office, has spent the majority of his time since his November 8 defeat of Hillary Clinton sequestered in his New York headquarters building his cabinet.

On Thursday he announced Oklahoma Attorney General Scott Pruitt as head of the Environmental Protection Agency, infuriating many Democrats and climate change experts, then unveiled fast food executive Andy Puzder as labor secretary.

More than half his cabinet positions have now been filled, with 43 days to go before the Republican is sworn in as the 45th president of the United States, the oldest man ever inaugurated into the office.

But the president-elect took a break from cabinet interviews to fly to Ohio, which helped secure his shock November 8 victory, to meet privately with victims and first responders of a November 28 attack at Ohio State University.

The assailant, Abdul Razak Ali Artan, was shot and killed by police after driving into a crowd and then slashing several people with a knife. Officials said 11 people were treated for injuries.

Such meet-and-greet visits designed to offer comfort to ordinary Americans who have suffered are a staple of modern-day presidents, but it was a first for the former reality TV star who favored mass rallies on the campaign trail.

"These were really brave people, amazing people," Trump told reporters in Columbus of the victims and their families.

"The police and first responders were incredible," he added. "The families have done so well to come through this so well and so, a lot of respect."

- 'Put off' -

Trump tweeted last week after the attack that Artan, who migrated from Somalia, should not have been in the country. He caused alarm during the election campaign by calling for a ban on Muslims entering the country.

Investigations into the motive are ongoing. Artan reportedly referred to Al-Qaeda teachings on Facebook. A jihadist-linked news agency called him a "soldier" of the so-called Islamic State group fighting in Iraq and Syria.

It was not immediately clear how many people met with the president-elect.

At least one of the victims refused to attend. Professor William Clark told CNN that he didn't feel the need from a "healing standpoint" and that he was "frankly a little put off" by Trump's initial reaction in blaming immigration.

"I've been a professor for 35 years and I know these issues when students do these kind of things they're often usually a lot more complex than that," he told the TV network.

Trump arrived in Columbus just as the death was announced in the city of John Glenn, 95, a former Ohio senator who made history as the first American to orbit the Earth.

The president-elect paid tribute to the former Democrat, calling him a "great pioneer of air and space" who had inspired generations of future explorers.

"To me he was a great American hero," Trump told reporters.

- Extreme edge -

Before setting off for the Midwest, Trump triggered a storm of criticism by tapping a fossil fuel ally to head the Environmental Protection Agency (EPA) -- outraging many who fear that he will reverse President Barack Obama's efforts to combat climate change.

In announcing the nomination of Pruitt -- who will need Senate approval -- Trump complained that "for too long," the EPA had spent "taxpayer dollars on an out-of-control anti-energy agenda that has destroyed millions of jobs."

Pruitt "will reverse this trend and restore the EPA's essential mission of keeping our air and our water clean and safe," the president-elect said.

"Scott Pruitt has spent the past several years fighting tooth and nail to help polluters erase or circumvent the critical environmental protections our nation has put in place," said Steny Hoyer, the number two Democrat in the House of Representatives.

Ken Kimmell, president of the Union of Concerned Scientists, described Pruitt as someone "on the outer extreme edge, and putting him in charge of EPA could really have devastating consequences."

While campaigning, Trump said Obama's environmental regulations were hamstringing US businesses and vowed to roll back regulations and slash corporate taxes in an effort to drive job creation and business growth.

But he also courted opinion from across the aisle, meeting this week with former Democratic vice president-turned-climate campaigner Al Gore and actor Leonardo DiCaprio, who is an active environmentalist.

The Hollywood star presented Trump, his daughter Ivanka and other aides with a plan to unleash "a major economic revival" through investments in sustainable infrastructure, said the chief executive of the Leonardo DiCaprio Foundation.

Later Thursday, Trump will travel to Des Moines to headline a "thank you" rally with Vice President-elect Mike Pence, following similar events in Cincinnati and North Carolina.

A new poll published by the Pew Research Center found that 40 percent of respondents approve of Trump's cabinet choices, compared to 71 percent for Obama's in December 2008 and 58 percent for George W. Bush's in 2001.