President Barack Obama has said that users of marijuana in states that have legalised its recreational use will not be a "top priority" of federal prosecutors.

In an interview with Barbara Walters of ABC News, Obama said law enforcement agencies had "bigger fish to fry" than to go after users in Washington and Colorado, where voters approved the legalisation of marijuana on election day.

Use of the drug remains prohibited under federal laws, and in his interview, Obama said he has asked the attorney general, Eric Holder, to examine how state and federal laws can be reconciled.

"It would not make sense for us to see a top priority as going after recreational users in states that have determined that it's legal," Obama said.

Last week, Washington became the first state to allow recreational use of marijuana, after voters sanctioned the move in the November ballot. Colorado will follow suit next month, when laws formally decriminalising the possession of marijuana take effect. Both states are examining how to regulate the legal sale of marijuana.

At a federal level, the Controlled Substances Act lists cannabis in the same category as heroin, LSD and ecstasy. Obama acknowledged that the discrepancy between the federal stance and that of Washington and Colorado will need to be addressed. "This is a tough problem because Congress has not yet changed the law," he told Walters in excerpts of the interview posted on the ABC website.

He added: "I head up the executive branch, we're supposed to be carrying out laws. And so what we are going to need to have is a conversation about, how do you reconcile a federal law that still says marijuana is a federal offence and state laws that say that it is legal?"

During the interview, Obama also touched upon his own views on recreational drug use.

In his 1995 memoir Dreams from My Father, Obama spoke of his past use of both marijuana and cocaine. At high school he was part of a group known as the Choom Gang, so-named for their fondness of pot smoking.

"There are a bunch of things I did that I regret when was a kid," he told Walters.

He added that he did not support a wholescale change in the law "at this point" and that he was not an advocate of marijuana use. "My attitude is, substance abuse generally is not good for our kids, not good for our society," Obama said, adding: "I want to discourage drug use."