- President: decision was step to rectifying 'unfair system'

- Each had already served more than 15 years in prison

- Obama signed the Fair Sentencing Act three years ago

Barack Obama reduced the sentences of eight people convicted of crack cocaine offences on Thursday, using his power of clemency to make statement about what the administration believes is an overly punitive criminal justice system.

The president said that his decision to commute the sentences was a small step toward rectifying an "unfair system" which has resulted in thousands of inmates receiving lengthy terms, raising hopes of a renewed push by the administration to reform the country's criminal justice system.

Three years ago, Obama signed the Fair Sentencing Act, a law which significantly narrowed the enormous disparity in sentences for crack and powder cocaine offences. But it did not apply retrospectively. Obama acknowledged on Thursday that "for thousands of inmates, [the law] came too late", and said the eight men and women to whom he offered clemency had each already served more than 15 years in prison.

"If they had been sentenced under the current law, many of them would have already served their time and paid their debt to society," Obama said in a statement. "Instead, because of a disparity in the law that is now recognised as unjust, they remain in prison, separated from their families and their communities, at a cost of millions of taxpayer dollars each year."

He added that in several of the cases "sentencing judges expressed frustration that the law at the time did not allow them to issue punishments that more appropriately fit the crime".

There has been a 500% increase in the number of inmates in federal custody in the US over the last three decades, leading to dangerous overcrowding in prisons, in part because of federally mandated sentences for nonviolent crimes.

All of the eight prisoners whose sentences have been commuted were convicted for drug offences that did not involve violence. Most will now be will be released in April, and one, Ezell Gilbert, from Florida, who was convicted in 1997 for possession with intent to distribute cocaine and marijuana, will be released immediately.

Perhaps the most prominent case among them is that of Clarence Aaron, who was convicted in Mobile, Alabama, for his role introducing an old high school friend to another friend whose brother was a cocaine dealer. Aaron was present during a drug transaction, and received three life terms, even though it was his first offence and he did not personally buy, sell or supply drugs.

Julie Stewart, president of Families Against Mandatory Sentences, which has campaigned for the release of Gilbert, Aaron and others on the clemency list, said the group was "glad that President Obama recognised that these individuals were serving unnecessarily lengthy sentences".

"The bottom line, however, is that there are several thousand more where they came from," she said. Stewart said that before Thursday's announcement, Obama had received over 8,700 commutation requests from federal prisoners and granted only one - Eugenia Jennings, who received a 22-year sentence for selling a small amount of crack cocaine. Jennings was ill with leukemia when her sentence was commuted, ten years into her sentence, and died two months ago.

Alongside the commutations, Obama also announced 13 pardons for people who had served their sentences for various offences, around half of which were related to drugs.

But it is the reduced sentences that attracted most attention among justice reform campaigners. To date, Obama has used his clemency powers far less than other presidents. Thursday's announcement marks the first time a president has commuted sentences of a group of inmates who would have received much shorter sentences had they received their punishments under current laws and sentencing policies.

In part, that is because Congress only significantly reduced drug sentences for the first time in 2011.

The eight cases constitute only a small fraction of the thousands of cases of disproportionate sentences cited by campaigners, in which men and women, often from deprived communities, have been sentenced to a lifetime behind bars for drug-related mistakes made when they were young and desperate.

Those granted shorter sentences include Stephanie Yvette George, who was sentenced to life in prison without parole for allowing her boyfriend to stash crack and drug paraphernalia at her home. The penalty was automatically levelled because of previous drug offences.

Sentencing George in 1997, Judge Roger Vinson appeared to acknowledge the unfairness of the punishment, telling her: "I wish I had another alternative ... your role has basically been as a girlfriend and bag holder and money holder. So certainly, in my judgment, it doesn't warrant a life sentence."

Another inmate granted freedom through Obama's clemency is Reynolds Allen Wintersmith, who was convicted in 1994 for his role dealing crack cocaine in his neighbourhood in Rockford, Illinois, three years earlier, aged just 17.

The others were Helen Alexander Gray, convicted for cocaine offences in Georgia in 1996, Jason Hernandex-McKinney, who received a life sentence for various drug offences in 1998, Ricky Eugene Patterson, imprisoned for life for cocaine offences in 1998 and Billy Ray Wheelock, who received a life sentence in 1993 for conspiracy to distribute more than 50 grams of crack cocaine and related offences.

The clemency offered by Obama raised hopes among justice reform groups that the White House would prioritise the issue in the coming years, possibly in his State of the Union address at the end of January.

Vanita Gupta, deputy legal director of the American Civil Liberties Union, said while she was "thrilled" that Obama had shown the political courage to issue eight pardons, "we know there are thousands of people languishing behind bars right now with life sentences for non-violent sentences".

However she expressed hope that Obama's announcement signalled a renewed effort by the administration to make lasting reforms.

In August the attorney general, Eric Holder, unveiled plans to enable non-violent drug offenders to avoid hard mandatory minimum sentences. Next month, the US Sentencing Commission is expected to release the findings of a sweeping of federal sentences review that could possibly pave the way to lower prison-terms for drug offenses.

The Senate Judiciary Committee is considering broader reform to mandatory minimum sentences, including a bill sponsored by Republican Senator Mike Lee and Senator Richard Durbin, the second-ranking Democrat. The bill seeks to alleviate pressure on America's overcrowded prisons.

In part, this would be done by allowing judges to use discretion and sentence below the federally mandated punishment in some non-violent offences.

In his statement, Obama hinted he would lend his weight to more comprehensive reform. "Commuting the sentences of these eight Americans is an important step toward restoring fundamental ideals of justice and fairness," he said. "But it must not be the last. In the new year, lawmakers should act on the kinds of bipartisan sentencing reform measures already working their way through Congress."