More than 5,500 inmates are set to go free in November in the largest one-time release of federal inmates in US history. As many as 40,000 prisoners could be released in coming years.

The US Sentencing Commission, an independent policy panel, voted last year to retroactively apply lower sentences for those convicted of drug-related felonies. On average sentences are being cut by an average of 25 months among federal inmates.

Obama presses to reduce prison population

Two years ago, President Barack Obama's Justice Department directed federal prosecutors to avoid seeking mandatory minimum sentences - which limit the discretion of judges to impose shorter sentences - for nonviolent drug offenders, as part of a broader initiative to reduce the country's incarceration rate.

The US has the largest prison population on the planet. There are 206,000 inmates in federal prisons, up from about 25,000 in 1980, according to the US Bureau of Prisons.

There were a total of 1.56 million inmates in federal and state prisons at the end of 2014, according to public figures from the US Department of Justice.

Reform advocates have long criticized sentencing disparities rooted in 1980s War on Drugs legislation that targeted crack cocaine and overwhelmingly jails minorities in troubled city centers.

A drug policy advocacy group welcomed the move but said it was no substitute for structural reform.

"Congress still needs to pass comprehensive criminal justice reform," Michael Collins of the Drug Policy Alliance said in a statement.

jar/jr (AP, Reuters)