WASHINGTON (AFP) - US President Barack Obama granted clemency Monday to 46 convicted drug traffickers, saying their original sentences were unduly harsh under outdated laws.

Obama has issued commutations before, mostly to non-violent drug offenders, but not in such a large number.

"I am commuting the sentences of 46 prisoners who were convicted many years - or in some cases decades - ago," said Obama in a video released by the White House.

"These men and women were not hardened criminals, but the overwhelming majority had been sentenced to at least 20 years... for non-violent drug offenses."

The move comes as part of the Obama administration's effort to reform the criminal justice system.

"So their punishment did not fit the crime. And if they had been sentenced under today's laws, nearly all of them would have already served their time," he added.

"I believe these folks deserve their second chance."