Attorney General Jeff Sessions has claimed legal cannabis causes violent crime, despite a lack of evidence for his claim.

Mr Sessions said the Justice Department will try to adopt "responsible policies" for enforcement of federal anti-marijuana laws.

He added that he believes violence surrounds the sale and use of the drug in the US.

“I believe it’s an unhealthy practice, and current levels of THC in marijuana are very high compared to what they were a few years ago, and we’re seeing real violence around that,” the attorney general said.

“Experts are telling me there’s more violence around marijuana than one would think and there’s big money involved."

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While stopping short of saying what he would do, Mr Sessions said he doesn't think America will be a better place with "more people smoking pot."

"I am definitely not a fan of expanded use of marijuana," he added. "But states, they can pass the laws they choose. I would just say, it does remain a violation of federal law to distribute marijuana throughout any place in the United States, whether a state legalises it or not."

Studies have found no correlation between the legalisation of marijuana and violent crime rates.

However, law enforcement officials in states such as Colorado say drug traffickers have taken advantage of lax marijuana laws to hide in plain sight, illegally growing and shipping the drug across state lines, where it can sell for much higher.

Pot advocates say officials have exaggerated the problem.

Hollywood sign changed to ‘Hollyweed' to promote cannabis legalisation

"You can't sue somebody for a drug debt," Mr Sessions said. "The only way to get your money is through strong-arm tactics, and violence tends to follow that."

His comments were in keeping with remarks made last week by White House spokesman Sean Spicer, who said the Justice Department would step up enforcement of federal law against recreational marijuana.

Eight states and the District of Columbia have legalised marijuana for recreational use.

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The Justice Department has several options available should it decide to enforce the federal law, including filing lawsuits on the grounds that state laws regulating pot are unconstitutional because they are pre-empted by federal law.

Mr Sessions said he met with Nebraska's attorney general, who sued Colorado for allegedly not keeping marijuana within its borders.