America’s top law enforcement official has announced significant changes to the Obama administration’s approach to drug enforcement, in a bid to curb the overcrowding of the nation’s prisons.

In a speech at the annual meeting of the American Bar Association in San Francisco on Monday, US Attorney General Eric Holder said he would order prosecutors to omit details of drug quantities from low-level indictments in future, to circumvent the federal law that imposes minimum sentences according to the volume of drugs involved.

A charge of conspiring to sell 5kg of cocaine, for example, carries a mandatory minimum sentence of 10 years. If prosecutors fail to mention the size of the haul, however, judges will be free to mete out lesser sentences.

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The move is designed to decrease government spending on the US prison system, which incarcerates around 25 per cent of the world’s prisoners.

"Too many Americans go to too many prisons for far too long and for no good law enforcement reason,” Holder said.