US President Joe Biden has commuted the sentences of 37 out of 40 federal death row inmates, switching their penalty to life in prison without parole.

The three excluded from the measure include the Boston Marathon bomber and the man who killed Jewish worshippers in 2018.

In a statement, Biden said he was "more convinced than ever that we must stop the use of the death penalty at the federal level". His measure does not include more than 2,000 people convicted to death by State authorities.

Biden's decision comes before the return of President-elect Donald Trump in January, who resumed federal executions when he was in office.

• Biden issues 39 presidential pardons and commutes 1,500 sentences

Among those reprieved by Biden are nine people convicted of murdering fellow prisoners, four for murders committed during bank robberies and one who killed a prison guard.

"Make no mistake: I condemn these murderers, grieve for the victims of their despicable acts, and ache for all the families who have suffered unimaginable and irreparable loss," Biden added.

Disgraced former New Orleans police officer Len Davis, who operated a drug ring involving other officers and arranged a woman's murder, is among those who have been shown clemency.

The three remaining on death row include Dzhokhar Tsarnaev, who helped carry out the 2013 Boston Marathon bombing, and avowed white supremacist Dylann Roof who shot and killed nine Black churchgoers in Charleston, South Carolina in 2015.

Robert Bowers, who killed 11 Jewish worshippers during a mass shooting in 2018 at the Tree of Life synagogue in Pittsburgh, will also remain on death row.

Biden has campaigned as an opponent of the death penalty, and the Justice Department issued a moratorium on its use at the federal level after he became president.

During his first term in office, Trump oversaw 13 deaths by lethal injection during his final six months in power.

There had been no federal inmates put to death in the US since 2003 until Trump resumed federal executions in July 2020.

During his re-election campaign, Trump indicated he would expand the use of capital punishment to include human and drug traffickers, as well as migrants who kill American citizens.

Biden appeared to refer to Trump's intentions in his statement by saying he could not "in good conscience - stand back and let a new administration resume executions that I halted".

In US law, these clemency decisions cannot be reversed by a president's successor.

Biden's decision will not impact people sentenced to death in state courts, which is around around 2,250 inmates according to the Death Penalty Information Centre. More than 70 state executions have been carried out during Biden's presidency.

The death penalty has been abolished in 23 of the 50 US states. Six other states, including Arizona, California, Ohio, Oregon, Pennsylvania and Tennessee, have moratoriums in place.

Earlier this month, Biden commuted the sentences of nearly 1,500 people and pardoned 39 more convicted of nonviolent crimes.

He also pardoned his son, Hunter Biden, who was facing sentencing for two criminal cases. He had pleaded guilty to tax charges earlier in September and was found guilty of being an illegal drug user in possession of a gun in June - becoming the first child of a sitting president to be convicted of a crime.

The US Constitution decrees that a president has the broad "power to grant reprieves and pardons for offences against the United States, except in cases of impeachment".