Image copyright Getty Images Image caption About one third of inmates being released are foreign citizens who will be deported

Roughly 6,000 federal inmates will be released in the coming weeks in an effort to ease prison crowding and lessen harsh penalties for non-violent offenders, US media report.

The release is the biggest of its kind in US history, the Washington Post reported.

The inmates being released early were all convicted of drug-related charges.

An additional 8,500 inmates will be eligible for release starting in November.

The US Sentencing Commission unanimously approved the reductions to the jail terms of inmates last year.

Up to 46,000 of the nation's about 100,000 drug offenders could qualify for early release under the commission recommendations.

These 6,000 prisoners are the first wave of early releases. Most of the those released will see about two years trimmed from their original prison terms.

"Even with the Sentencing Commission's reductions, drug offenders will have served substantial prison sentences," Deputy Attorney General Sally Yates told the Post.

Image copyright Getty Images Image caption About 46,000 inmates convicted of non-violent drug crimes could eventually be released

About one-third of the inmates up for release are foreign citizens. They will be quickly deported, officials said.

President Barack Obama's administration has been working to tackle what he sees as a lack of fairness in the system.

The planned releases continue a drive that started in 2013 when US Attorney General Eric Holder dropped mandatory minimum sentences for non-violent drug offenders.

Many leading Democrats and Republicans now believe that mandatory prison sentences that led to mass incarceration in the US have not been effective.

The US has almost a quarter of the world's prison population - one in every 99 Americans is behind bars.

Media playback is unsupported on your device Media caption Why are so many Americans behind bars?

"Far too many people have lost years of their lives to draconian sentencing laws born of the failed drug war," Jesselyn McCurdy, a senior legislative counsel at the American Civil Liberties Union told the New York Times. "We are overjoyed that some of the people so wronged will get their freedom back."

However, others are concerned that such a large prisoner release could lead to an uptick in crime in the US.

Many US cities have seen homicide rates in increase over the past year and some law enforcement officials worry a surge of ex-convicts could exacerbate that trend.