Image caption Advocates of marijuana for medical purposes now want to hold a referendum to overturn the ban

A US medicinal marijuana trade group is suing the city of Los Angeles to try to stop it from enforcing a ban that would close hundreds of dispensaries.

The Patient Care Alliance Los Angeles (PCA-LA) says users are protected by California's 1996 legalisation of medicinal marijuana.

The LA city council last month passed a law to ban the dispensaries.

It said the use of the drug was spiralling out of control, leading to an increase in crime in the city.

"The city council's actions are not only reckless, heartless and pointless, they're just plain stupid," Marc O'Hara of PCA-LA was quoted as saying by the NBC News.

"The city knows that it will never be able to successfully defend this lawsuit," he added.

City politicians unanimously approved the ban on 24 July.

The vote followed complaints that young people had too easy access to the drug and were illegally using it for recreational purposes, in turn leading to an increase in crimes in areas where marijuana was for sale.

Earlier this week, the council sent out letters to locations where dispensaries were thought to be operating, stating that such businesses would become illegal on 6 September.

Meanwhile, advocates of marijuana for medical purposes have pledged to push for a referendum to try to overturn the ban.

Many dispensaries in Los Angeles have recently been gathering signatures in support of the ballot.