Juneteenth celebrations marking the end of slavery in the United States were being held across the country on Friday with the holiday taking on added significance this year amid nationwide protests for racial justice.

In a stark illustration of the tensions roiling the nation, President Donald Trump issued a solemn statement commemorating Juneteenth while at the same time threatening protestors on Twitter.

Juneteenth, the annual US commemoration of the end of slavery, comes as Americans continue Black Lives Matter demonstrations and protests against police brutality following two high-profile killings of blacks by police in May and June, 2020
Juneteenth, the annual US commemoration of the end of slavery, comes as Americans continue Black Lives Matter demonstrations and protests against police brutality following two high-profile killings of blacks by police in May and June, 2020 AFP / CHANDAN KHANNA

Juneteenth marks the day -- June 19, 1865 -- when a Union general arrived in Galveston, Texas, and informed slaves that they were free -- two months after the Civil War had ended and two-and-a-half years after president Abraham Lincoln had issued the Emancipation Proclamation.

Demonstrations, prayer services and cultural celebrations of food and music will be held from New York to Chicago to Los Angeles to honor the day.

This year's celebrations come against a backdrop of protests for racial justice fueled by the May 25 death of George Floyd, a 46-year-old black man killed by a white police officer in Minneapolis, Minnesota.

A woman walks past a street mural by artist Vincent Ballentine on June 16, 2020 in the New York borough of Brooklyn as racial tensions simmer in the United States
A woman walks past a street mural by artist Vincent Ballentine on June 16, 2020 in the New York borough of Brooklyn as racial tensions simmer in the United States AFP / Angela Weiss

Several commemorations have gone virtual to account for the coronavirus pandemic, but many are going ahead as planned or with modifications such as social distancing and mask-wearing guidelines.

Trump scheduled a re-election campaign rally on Juneteenth in Tulsa, Oklahoma, his first since the pandemic began.

But he was forced to change it to Saturday amid an outcry over his provocative choice of date and location -- Tulsa suffered one of the country's worst racist massacres, in 1921, when as many as 300 black Americans were killed.

Several Confederate statues have been toppled or ordered removed across the United States, including one of president of the Confederacy Jefferson Davis, whose statue was pulled down by protesters in Richmond, Virginia
Several Confederate statues have been toppled or ordered removed across the United States, including one of president of the Confederacy Jefferson Davis, whose statue was pulled down by protesters in Richmond, Virginia AFP / Parker Michels-Boyce

The Republican president and First Lady Melania Trump issued a joint statement on Friday to mark Juneteenth.

People praying during a Juneteenth event at Centennial Olympic Park in Atlanta, Georgia
People praying during a Juneteenth event at Centennial Olympic Park in Atlanta, Georgia GETTY IMAGES / JOE RAEDLE

"Juneteenth reminds us of both the unimaginable injustice of slavery and the incomparable joy that must have attended emancipation," it said.

"This Juneteenth, we commit, as one Nation, to live true to our highest ideals and to build always toward a freer, stronger country that values the dignity and boundless potential of all Americans."

In honor of Juneteenth, the World Bank Group displayed an 'End Racism' banner on their headquarters in Washington
In honor of Juneteenth, the World Bank Group displayed an 'End Racism' banner on their headquarters in Washington AFP / JIM WATSON

At the same time, Trump issued a blunt warning to counter-protestors at his Tulsa rally.

"Any protesters, anarchists, agitators, looters or lowlifes who are going to Oklahoma please understand, you will not be treated like you have been in New York, Seattle, or Minneapolis," he said. "It will be a much different scene!"

Tulsa Mayor G.T. Bynum declared a curfew in the city which is to run until 6:00 am on Sunday, with a break for Trump's rally.

A man holds a picture of George Floyd during a Black Lives Matter protest in New York City
A man holds a picture of George Floyd during a Black Lives Matter protest in New York City GETTY IMAGES / Jeenah Moon

Nancy Pelosi, the Democratic speaker of the House of Representatives, also issued a statement commemorating Juneteenth.

"Sadly, this Juneteenth comes during a moment of extraordinary national anguish, as we grieve for the hundreds of Black Americans killed by racial injustice and police brutality," Pelosi said.

"This Juneteenth must be a day of reflection that moves our nation to finally confront and combat its long and shameful history of systemic racial injustice targeted at communities of color."

Pelosi also recalled that she had ordered the removal this week of portraits of leaders of the pro-slavery Civil War South from the US Capitol.

Monuments depicting Confederate generals or soldiers have been toppled by protesters or ordered removed by local governments in a number of US cities during the past few weeks.

Video of Floyd's death energized a quest for equality among African Americans who decry how systemic racism and injustice have been allowed to fester in the world's flagship democracy.

Millions of people have taken to the streets of cities in the US and beyond under the "Black Lives Matter" banner to protest racial injustice and police brutality.

Further fuelling tensions, a police officer in Atlanta last week shot dead a black man who was running away after a scuffle during a drunk-driving arrest.

Both offending officers in the incidents have been charged with murder, and the killings have spurred US lawmakers to introduce sweeping new police reforms.

In Washington, several streets have been closed to traffic and there was a strong police presence in the new "Black Lives Matter" plaza near the White House, where protesters were to converge in the afternoon.

In Tulsa, a day-long "I, Too, Am America" rally for justice is planned and the civil rights activist Al Sharpton is scheduled to give a speech.

Dozens of events are planned in New York including a march to City Hall demanding "justice, dignity and equality" for black Americans.

Chicago will host a "Black Lives Matter Block Party" featuring voter registration drives.

Pressure has mounted for Juneteenth to be declared a national holiday and New York and Virginia have moved to make it an official state holiday.

Several major US companies including Nike and Twitter recently announced they were making Juneteenth a paid holiday for employees.