President Donald Trump on Tuesday denied any racist "strategy" behind a string of verbal attacks on African-Americans, but found himself being accused of "hate" by a heckler at a high-profile speech.

"I have no strategy. I have zero strategy," Trump told reporters at the White House, when asked about his recent tirades against black and other non-white opponents, as well as the majority black city of Baltimore.

"I'm not angry at anybody," he said.

Earlier, Mr Trump denounced the "horrors" of slavery in a speech in Jamestown, Virginia, celebrating the founding of the first local legislature there by English colonists 400 years ago.

In his speech, Mr Trump noted that along with the first settlers came the first African slaves, making Jamestown a symbol not just of US democracy but of mass slavery.

"We remember every sacred soul who suffered the horrors of slavery," President Trump said, calling this the "barbaric trade in human lives."

But black Virginia state lawmakers boycotted the event, saying it had been "tarnished" by Mr Trump.

"It is impossible to ignore the emblem of hate and disdain that the president represents," the African-American lawmakers said in a statement, accusing Mr Trump of using "racist and xenophobic rhetoric."

And in a rare interruption of a presidential speech, a Virginia state lawmaker heckled Mr Trump and held up a sign reading "Deport hate" and "Go back to your corrupted home."

Trump paused his speech while the man was led away but did not say anything.

'Least racist'?

The president has shown little of that restraint over the last two weeks, with a barrage of racially loaded insults.

President Trump has laid repeatedly into four non-white Democratic congresswomen, a respected black Democratic lawmaker from Baltimore, as well as veteran black civil rights activist Al Sharpton.

That pattern has prompted an outpouring of criticism that Trump is deliberately deepening racial divisions in a pitch to his white, working-class base ahead of his 2020 reelection bid.

At the White House, he told reporters: "I am the least racist person anywhere in the world."

But he then claimed that Mr Sharpton is a racist and he continued to lash out at Baltimore.

Over the weekend, Mr Trump described Baltimore as a "rat and rodent infested mess" unfit for humans and blamed this on Elijah Cummings, the black Democrat who represents much of the city in Congress.

He then attacked Mr Sharpton for coming to Baltimore's defense, tweeting that "Al is a con man" who "Hates Whites & Cops!"

Mr Sharpton responded that Trump is a bigot with "venom for blacks."

Mr Trump denied Tuesday that the controversy, which breaks with all norms in Washington, has hurt him, claiming instead that residents from Baltimore were phoning en masse to thank him for calling out what he says is the city's disastrous leadership.

"African-American people have been calling the White House. They have never been so happy for what our president has done," he said.

The claimed flood of phone calls could not be independently verified. However, opinion polls show that support for Mr Trump among black voters nationwide is at rock bottom.