President Joe Biden has at last made lynchings in the United States a federal hate crime after more than a hundred years of delays.

US President Joe Biden has signed into law the first federal legislation that makes racist lynching a hate crime, putting an end to over a century of delays in outlawing what he called "pure terror."

The Emmett Till Anti-Lynching Act is named after a 14-year-old Black boy whose brutal murder in the southern state of Mississippi galvanized the US civil rights movement in the 1950s.

Biden signed the bill — which was passed by the Senate earlier this month — on Tuesday at a desk in the White House Rose Garden.

He was surrounded by Vice President Kamala Harris, members of Congress, top Justice Department officials, a descendant of Ida B. Wells, a Black journalist who reported on lynchings, and Rev. Wheeler Parker, a cousin of Till.

"Lynching was pure terror, to enforce the lie that not everyone, not everyone belongs in America, not everyone is created equal,'' the president said.

Those convicted under the law will face up to 30 years in jail.

The bill , which passed the Senate by unanimous consent and the House of Representatives by a vote of 422-3, ends a history of impunity over what researchers say were thousands of lynching between the the end of the Civil War in 1865 and 1950 — that often went unpunished.

Who was Emmett Till?

Till was visiting relatives in Mississippi where he was abducted and killed in August 1955.

A white woman had alleged that the boy had propositioned her in a store and touched her on the arm, hand and waist.

Days later, Till's mutilated body was found in a local river.

The boy's grieving mother had insisted on an open casket to show the world how her son had been brutalized.

The murder became a turning point in the civil rights era.

Two white men, Roy Bryant, Carolyn Bryant's husband, and J W Milam, his half-brother, were charged with murder but were subsequently acquitted by an all-white jury.

The men later admitted in an interview that they had murdered Till.

'Lynching not a relic of the past'

On Tuesday, Vice President Kamala Harris said that with the signing of the bill, the president was addressing both "unfinished business" and "horror" in America's history.

Harris, the nation's first Black and Asian American vice president, co-sponsored the bill while serving as a US senator from California.

"Lynching is not a relic of the past. Racial acts of terror still occur in our nation. And when they do, we must all have the courage to name them and hold the perpetrators to account," Harris said.

Biden also emphasized that forms of racial terror continue in the US, underlining a need for an anti-lynching statute.

"Racial hate isn't an old problem, it's a persistent problem,'' Biden said.

"Hate never goes away. It only hides.''