Image copyright Getty Images Image caption The sentences of most of those affected by the president's order will now end on 1 December

US President Barack Obama has cut short the jail sentences of 214 federal inmates, including 67 life sentences, in what officials say is the single biggest act of presidential clemency in more than 100 years.

Most of those affected were guilty of non-violent crimes, many involving possession or distribution of drugs.

The president has now made 562 commutations, officials say.

He has authorised more than the previous nine presidents combined.

Image copyright Getty Images Image caption It is estimated that some 47% of US prison inmates have been incarcerated for drug offences

Image copyright Reuters Image caption President Obama argues that some inmates in US jails have been behind bars for too long

Almost all the prisoners were convicted for crimes related to cocaine, methamphetamine or other drugs.

A few are in jail for firearms violations related to their drug activities. Almost all those affected are men, representing a diverse geographical cross-section of the US.

"All of the individuals receiving commutation [on Wednesday] were incarcerated under outdated and unduly harsh sentencing laws," White House counsel Neil Eggleston wrote in a blog post.

"They embody the president's belief that America is a nation of second chances."

Correspondents say that Mr Obama's drive to reduce the sentences of non-violent drug offenders as part of his clemency initiative reflects his long-held belief that the US needs to introduce less severe sentencing requirements.

The president is believed to have used the fast pace of his commutations to put pressure on Congress to address the sentencing issue.

One of the inmates benefitting from the president's leniency is reported by the AP news agency to be Dicky Joe Jackson of Texas.

He was sentenced to life in 1996 for methamphetamine violations and for being a felon with an unlicensed gun.

Jackson was reported to have said in 2013 that he would have preferred a death sentence: "I wish it were over, even if it meant I were dead,'' he was quoted as saying at the time.

The sentences of most of those affected by the president's order will now end on 1 December, officials say.