FILE - Inmates are seen exercising in the main yard at California State Prison in Vacaville, California, May 20, 2015.
FILE - Inmates are seen exercising in the main yard at California State Prison in Vacaville, California, May 20, 2015.

Thousands of U.S. federal inmates jailed for a variety of drug crimes will be released at the end of the month as new sentencing guidelines come into effect.

In April 2014, the U.S. Sentencing Commission voted to lower the federal drug sentencing guidelines as part of an effort to reduce prison overcrowding and curb excessive sentences. The new rules were set to affect to future drug sentences, but those changes were later applied to inmates already convicted.

Thousands of inmates have since petitioned to have their sentences revised under the guidelines and the first wave of prisoners ­estimated at close to 6,000- are set to be released by November 1. Most of them have already completed their sentences and will be released from halfway houses or home detention.

More than 45,000 federal prisoners will be eligible for sentence reductions in the coming years. 

As of August 2015, a total of 17,446 inmates applied for hearings, 13,187 or 75.6 percent were given reduced sentences while 4,259 or 24.4 percent were denied their requests. 

The sentencing commission says the majority of drug offenders eligible for release were convicted of distributing of methamphetamine (30.9 percent), followed by powder cocaine (27.2 percent) and crack cocaine (20.5 percent).

More than 3,000 of those granted reduced sentences are non-U.S. citizens with many expected to be deported after their release.

According to the non-profit organization, Families Against Mandatory Minimums, offenders eligible for a reduction could have their sentences reduced by an average of just over two years, serving nine years sentences, on average.

The sentencing changes does not affect mandatory minimums for drug cases, but rather the drug sentencing ranges, which in many cases is significantly higher than the minimum sentences.

In a statement Wednesday, a spokesman for United Nations Secretary-General Ban Ki-moon said he welcomed the decision for early release. "States should only apply deprivation of liberty as a measure of last resort and only after alternatives have been duly considered," said the statement. "Over-incarceration constitutes one of the major underlying causes of overcrowding, which results in conditions that can often amount to ill-treatment or even torture."

U.S. President Barack Obama, the first sitting pre
U.S. President Barack Obama, the first sitting president to visit a federal prison, speaks during his visit to the El Reno Federal Correctional Institution outside Oklahoma City, July 16, 2015.

Earlier this year, U.S. President Barack Obama met with law enforcement officials and nonviolent drug offenders at a federal prison in Oklahoma as part of his push for a fairer justice system and prison reform.

Obama called for either reducing or eliminating mandatory minimum sentences for non-violent drug crimes, reconsidering solitary confinement for prisoners and increasing job training programs for people while they are incarcerated.

The president has said that overly harsh sentences are responsible for the doubling of the U.S. prison population in the last 20 years.

He has urged Congress to pass a sentencing reform bill by year's end.

The United States is the world's largest jailer accounting for nearly 25 percent of the world's prison population despite making up just less than five percent of the world's population.

Some material for this report came from AP.