President Barack Obama's administration ceded ground Thursday in the US war on drugs, saying it will not dispute the legalization of recreational marijuana in Colorado and Washington state.
Its decision was swiftly hailed by campaigners for the legalization of a substance that, under federal law, remains a Schedule One controlled substance on a par with heroin.
In a statement, the Department of Justice said it expects Colorado and Washington to maintain "strict regulatory schemes" to ensure that marijuana doesn't profit criminal gangs or fall into the hands of minors.
"These schemes must be tough in practice, not just on paper," it said.
That said, the Department of Justice added that it has told the governors of Colorado and Washington that it is "deferring its right to challenge their legalization laws at this time."
Voters in Colorado and Washington approved the legalization of marijuana in referendums last November concurrent to the presidential election that kept Obama in the White House for a second term.
Several other states have approved the production and sale of marijuana for medicinal use, and decriminalized the possession of small quantities for personal use.
"Today's announcement is a major and historic step toward ending marijuana prohibition," said Dan Riffle of the Marijuana Policy Project, a marijuana policy organization.
He called the decision "a clear signal (from the nation's capital) that states are free to determine their own policies with respect to marijuana."
It was now up to Congress "to fix our nation's broken marijuana laws, Riffle added.
The National Cannabis Industry Association expressed confidence that marijuana-related businesses in Colorado and Washington will comply with any federal requirements.
"We are pleased to see the Obama administration will not cause harm to citizens and states by shutting these businesses down," it said in a statement.
The US Attorney's Office in Colorado, elaborating on the Department of Justice's announcement, said it would still go after those who peddle marijuana to children, grow it on federal land or ship it across state or federal lines.
It would also target any marijuana trafficking that is either conducted or bankrolled by street gangs and cartels.
Earlier this year, for the first time, a majority of respondents to a Pew Research Center poll, 52 percent, said the use of marijuana should be made legal.
Forty-eight percent said they had consumed marijuana at some time in their lives, and 12 percent said they had done so in the year preceding the poll.