"Sometimes in the heat of debate, and speaking on a multitude of issues, you don't choose the right words or you say the wrong thing," Trump told an evening rally in North Carolina on Thursday.

"I have done that, and, believe it or not, I regret it," he said, adding "particularly where it may have caused personal pain."

His public feud with an American Muslim family whose son was killed while serving in the US military in Iraq did little positive for Trump's ailing campaign.

His trip to Charlotte, North Carolina - a Southern swing state - followed his announcement on Wednesday of a reshuffle of his campaign, with opinion polls showing him falling behind Clinton in decisive states, including North Carolina.

The shake-up brought in Stephen Bannon (pictured left), who runs the conservative website Breitbart News, to the role of chief executive, and Kellyanne Conway, a veteran Republican pollster, as campaign manager.

"We're going to sharpen the message," Conway told broadcaster "CNN" on Thursday.

"What I would like him to do is let everyone get the benefit of his leadership. He scores very well in strong leader, and that's what so many Americans are starving for."

Too little, too late?

Trump's campaign reportedly began placing television advertising Thursday in North Carolina, as well as Pennsylvania, Ohio and Florida - three other swing states, the website Politico reported. Trump will invest nearly $5 million in battleground state advertising.

Democrat Clinton has spent more than $75 million on advertising in 10 states since locking up her party's nomination.

Hitting new lines

Trump struck a new, inclusive tone by trying to appeal directly to non-white voters, shown by polls to an overwhelmingly unfavorable view of the candidate. "I will not rest until children of every color in this country are fully included in the American Dream," Trump told his audience, again accusing Clinton of "bigotry."

Clinton, he claimed, "sees communities of color only as votes and not as human beings worthy of a better future."

He urged African-American voters to give him a chance, saying: "What do you have to lose by trying something new?"

jbh/kl (dpa, AP)