Former US President Bill Clinton has publicly confessed that the crime measure he enacted back in 1994 when he occupied the country's top post only made the US criminal justice system worse, expressing remorse that the law only caused crime to rise.

Clinton said although the law he signed put more police officers to patrol the streets, the measure had mixed results, wrote CNN.

"I signed a bill that made the problem worse," Clinton said before an audience at the National Association for the Advancement of Colored People's annual meeting in Philadelphia. "And I want to admit it."

The omnibus measure that was supposed to tackle the issue of crime included the federal "three strikes" provision, which requires that life sentences be given to criminals convicted of a violent felony after two or more previous convictions, including drug crimes.

The former chief executive said he affixed his signature into the law because "we had had a roaring decade of rising crime" when he entered the White House.

"We had gang warfare on the streets. We had little children being shot dead on the streets who were just innocent bystanders standing in the wrong place," he said.

In answer to these, the measure increased the number of police officers on the streets and enacted gun control legislation.

However, decades later, Clinton believes the results of the law were mixed, at best, with the law making people linger in jails for too long.

"In that bill, there were longer sentences. And most of these people are in prison under state law, but the federal law set a trend," Clinton said.

"And that was overdone. We were wrong about that. That percentage of it, we were wrong about. "

Clinton said some people who only took on minor roles in some crimes were jailed for too long, The New York Times reported.

"The bad news is we had a lot of people who were essentially locked up who were minor actors for way too long."

This was not the first time Clinton apologised for his role on the burgeoning jail population in the US. Earlier this year, he said the 1994 law "cast too wide a net and we had too many people in prison."

"And we wound up ... putting so many people in prison that there wasn't enough money left to educate them, train them for new jobs and increase the chances when they came out so they could live productive lives," he said.

The measure did decrease the crime rate, posting the biggest fall in history.

"The good news is we had the biggest drop in crime in history," he said.

Clinton delivered his remarks amid the Democratic Party's greater focus on criminal justice reform.

President Barack Obama said he wanted to end the practice of mass incarceration, outlining his plan as he addressed the National Association for the Advancement of Colored People's convention on Tuesday.

"Mass incarceration makes our country worse off and we need to do something about it," Obama said.

Democrat presidential candidate Hillary Clinton has made criminal justice reform a staple of her campaign.

"Keeping them behind bars does little to reduce crime, but it does a lot to tear apart families," said the former first lady earlier this year in New York. "Our prisons and our jails are now our mental health institutions."

Both Clintons worked hard towards the enactment of the 1994 crime bill.

"We will finally be able to say, loudly and clearly, that for repeat, violent, criminal offenders: three strikes and you're out. We are tired of putting you back in through the revolving door," Hillary Clinton said back in 1994.