In his speech, Donald Trump paid tribute to the 1619 creation of the Jamestown assembly (File)

President Donald Trump denounced the "horrors" of slavery in a speech Tuesday marking the birth of US democracy, but an interruption by a heckler accusing him of "hate" underlined how many Americans now see him as openly racist.

A political firestorm over race has engulfed the Republican leader over the last week and the ugly controversy followed him to Jamestown, Virginia, where 400 years ago English colonists established their first local legislature.

Black Virginia state lawmakers boycotted the event, saying it had been "tarnished" by 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 Trump of using "racist and xenophobic rhetoric."

In his speech, Trump paid tribute to the 1619 creation of the Jamestown assembly, set up to rule the nascent English colony -- a forerunner of the democratic US state.

He also noted that along with the first settlers came the first African slaves, making Jamestown a symbol not just of liberty but mass slavery.

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

Trump also stressed that it took civil war to end slavery in 1865 and another century for the civil rights movement to end blatantly racist policies against African-Americans.

But the Republican president faces mounting accusations of pushing racism of his own with tirades against immigrants and prominent non-white politicians.

In a rare interruption of a presidential speech, a Virginia state lawmaker heckled 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 showed little of that restraint barely an hour earlier, when he used remarks to White House reporters to pursue his racially loaded feuding.

Over the past two weeks, Trump has laid repeatedly into four non-white Democratic congresswomen, a respected black Democratic lawmaker from Baltimore, and veteran 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 insisted: "I am the least racist person anywhere in the world."

But he then claimed that Sharpton is a racist and he continued to lash out at the majority black, Democratic-led city of Baltimore.

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

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

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

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 of himself.

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