But officials will allow more research into its possible medical benefits, the Drug Enforcement Administration has announced.

The DEA said the agency opted not to reclassify marijuana after a lengthy review and consultation with the Health and Human Services Department, which said marijuana "has a high potential for abuse" and "no accepted medical use".

"We are tethered to science and bound by statute," DEA spokesman Rusty Payne said.

The decision to keep marijuana in the same class of drugs as heroin and peyote comes amid growing national support for the legalisation of marijuana.

More than half the states have legalised the drug for either medicinal or recreational use.

The DEA said it plans to make it easier for researchers to study marijuana's possible medical benefits by expanding the number of entities that can legally grow marijuana for research purposes.

Currently only researchers at the University of Mississippi are allowed to grow marijuana, as part of a contract with the National Institute on Drug Abuse.

Allowing for further research is the latest step forward in the federal government's evolving position on marijuana, although legalisation advocates claim it does not go far enough.

The DEA's latest review of marijuana's classification was prompted by requests from the former governors of Rhode Island and Washington.

They requested that marijuana be considered a Schedule II drug, along with cocaine, morphine and opium

The decision was announced in a lengthy notice in the Federal Register.