Copenhagen city officials said Friday they want to legalise the sale of cannabis for a trial period in order to better control the sale and consumption of the drug.

"A controlled legalisation would open the door to new solutions that would limit the bad effects and reduce some of the social problems that a failed policy of banning the substance has brought with it," Copenhagen's mayor for social affairs Mikkel Warming told a city council conference on the issue.

Any move to legalise the use of cannabis would require government and parliamentary support, but a similar appeal a year ago for a trial run of a "Copenhagen Model" was turned down by the justice ministry and received little or no support from national parties.

Warming said he would nonetheless be reapplying to the ministry to be allowed to introduce the Copenhagen Model for a trial period.

Under the model, cannabis would not be sold to persons under the age of 18, would be sold either from an existing chain of shops or from a local council shop and would be controlled.

"In order not to foster greater consumption, sales locations should not be attractive and not foster a special culture or atmosphere that would attract new users," the council plan said, adding that "the programme must not result in hash tourism".

The council said it envisaged only Danish citizens being allowed to buy the products, which would be available in various strengths and with full product information and declaration.

"Legalisation would give us much more contact with people who have problems of addiction. It will also make sure that hash is hash and not some mixture of rubber, glass and other poisonous content," Warming said.

He acknowledged that the trial outcome may not be positive.

"For example we don't know if legalisation will increase consumption and we don't know how socially and psychologically vulnerable people will react," Warming said.

Another challenge foreseen in the programme was how to get hold of an internationally illegal substance to sell. The city suggested possibly importing hash from "producers of hash for medicinal purposes from Washington or Colorado," though no approaches have been made to US authorities.

Currently, the sale and importation of cannabis in Denmark is illegal, though the black market is estimated at some one billion kroner (134 million euros, $175 million) annually.