Dustin Higgs, an inmate on death row in Indiana, has died in the final federal execution of the Trump presidency just days before he leaves office.

Higgs was convicted in the killings of three women in a wildlife refuge in 1996, but until his death denied ordering their murder.

He died by lethal injection at 01:23 local time (06:23 GMT) on Saturday.

His execution is the 13th carried out since July when the US government ended a 17-year hiatus on federal executions.

It comes just days before President-elect Joe Biden, who is against the death penalty, is sworn in.

There has been criticism of the Trump administration's rush to carry out the sentences - breaking with a 130-year-old precedent of pausing executions during a presidential transition.

What was Dustin Higgs convicted of?

Higgs was convicted and sentenced to death in 2001 for overseeing the 1996 kidnapping and murder of three women: Tanji Jackson, Tamika Black and Mishann Chinn.

The women had been on a date with Higgs and two other men at an apartment before one rebuffed his advances and an argument broke out between the group. Higgs and accomplice Willis Haynes offered to drive them home but instead took them to a wildlife refuge in Maryland, where prosecutors said Higgs gave Haynes a gun and told him to shoot the three women.

Haynes, who confessed to being the shooter, was sentenced to life in prison in a separate trial.

"It is arbitrary and inequitable to punish Mr Higgs more severely than the actual killer," a lawyer had appealed in a plea for clemency addressed to President Trump.

A court had ordered a stay of execution for Higgs and another inmate, Corey Johnson, on Tuesday after they contracted Covid-19 on death row - with lawyers arguing damage to their lung tissue would cause painful suffering during their executions.

But the Department of Justice immediately appealed and won the case. Johnson was put to death on Thursday.

A final bid to halt Higgs's execution then failed on Friday when the US Supreme Court's conservative majority voted 6-3 to clear the way the sentence to be carried out.

"This is not justice," Justice Sonia Sotomayor wrote in her dissent. "After waiting almost two decades to resume federal executions, the Government should have proceeded with some measure of restraint to ensure it did so lawfully. When it did not, this Court should have. It has not."

She also listed the names of all 13 executed since July: "To put that in historical context, the Federal Government will have executed more than three times as many people in the last six months that it had in the previous six decades."

In his final words, Higgs repeated his claim to innocence.

"I'd like to say I am an innocent man," he said, mentioning the three women by name. "I did not order the murders."

Higgs was the third to die at a federal prison in Terre Haute, Indiana this week including Lisa Montgomery, the only woman on federal death row on Wednesday.

"The government completed its unprecedented slaughter of 13 human beings tonight by killing Dustin Higgs, a Black man who never killed anyone, on Martin Luther King's birthday," Shawn Nolan, one of Higgs's lawyers, said in a statement.

"Dustin spent decades on death row in solitary confinement helping others around him, while working tirelessly to fight his unjust convictions."