The US has for the first time in almost two decades executed a federal inmate on death row by lethal injection.

Convicted murderer Daniel Lee Lewis, 47, pleaded for his life just moments before he was administered the deadly drug pentobarbital.

It came after an overnight ruling by the Supreme Court cleared the way for the US government to carry out its first execution in 17 years.

“I didn’t do it,” Lee said just before he was put to death. The former white supremacist and an accomplice were convicted of killing three members of an Arkansas family in 1996.

Strapped to a gurney, Lee continued: “I’ve made a lot of mistakes in my life but I’m not a murderer. You’re killing an innocent man.”

As the drug was being administered, Lee raised his head to look around, and his breathing appeared to become laboured.

Soon after, Lee’s chest was no longer moving, his lips turned blue and his fingers became ashy.

Lee was pronounced dead at 8.07am local time on Tuesday, a US Bureau of Prisons spokeswoman said.

His death marked the culmination of a three-year effort by US President Donald Trump’s administration to resume capital punishment.

Daniel Lewis Lee, 47, of Yukon, Oklahoma, died by lethal injection at the federal prison in Terre Haute, Indiana. Lee killed an Arkansas family in a 1990s in a plot to build a whites-only nation in the Pacific Northwest. https://t.co/a00TSN3zDP

— The Associated Press (@AP) July 14, 2020

US Attorney General William Barr endorsed the execution in a statement.

“The American people have made the considered choice to permit capital punishment for the most egregious federal crimes, and justice was done today in implementing the sentence for Lee’s horrific offences,” he said.

The Supreme Court in a 5-4 vote cleared the way for federal executions to resume, ruling that Lee and other condemned men’s challenges to the execution protocol did not justify “last-minute” intervention by federal courts.

The execution in Terre Haute, Indiana, was preceded by a flurry of legal challenges in multiple federal courts.

Ruth Friedman, one of the public defenders who represented Lee, rebuked the Department of Justice for what she described as a rushed process.

In a statement, she said it was “beyond shameful that the government, in the end, carried out this execution in haste, in the middle of the night, while the country was sleeping”.

The victims’ relatives unsuccessfully sued last week to delay the execution until the coronavirus pandemic had passed, saying they feared attending would risk their safety.

Lee’s accomplice Chevie Kehoe was sentenced to life in prison.

-with AAP