Almost half of Rotterdam's coffee shops, where marijuana can be sold, have been told to close down because they are located within 250 meters of a secondary school or a college, Dutch paper De Volkskrant reported Friday.

Rotterdam authorities said Thursday that secondary school children and college students should not be exposed to the temptation of smoking marijuana. As a result, in total 27 of Rotterdam's 62 coffee shops have to close down.

The measure is a consequence of the new Dutch coffee shop policy which is to take effect on January 1 2009, the report said. As of that date, no soft drugs -- such as marijuana, which are considered to be only psychologically addictive -- can be sold within 250 meters of schools.

Rotterdam Mayor Ivo Opstelten said Thursday that the use of soft drugs by groups of "vulnerable" youngsters is on the increase and problems have also arisen due to drug dealing and use.

Besides closing down coffee shops near schools, the Rotterdam authorities will tighten up surveillance, introduce information campaigns in schools on the dangers of drug use, and impose stricter conditions for obtaining a licence to run a coffee shop.

A tougher line will also be taken with regard to illegal drug sales on the street.

However,experts have doubts about the effectiveness of the measures.They say that school children who are not allowed in coffee shops under current rule usually ask their friends to buy soft drugs for them. And the new measures will do nothing to alter this.

All drugs are technically illegal in the Netherlands, but cities may license the so-called coffee shops to sell "soft drugs" like marijuana or hashish. People are not prosecuted for possession of small quantities of soft drugs for personal use.

The coffee shops may not sell to anyone under 18, and each customer may be sold no more than 5 grams per day.

The Dutch government hopes such a drug policy can help separate the markets for soft drugs and hard drugs -- like cocaine and heroin -- so that soft drug users are less likely to come into contact with hard drugs.