The Gulf emirate of Dubai on Saturday banned the sale of tobacco to anyone under the age of 20 with immediate effect and barred young people from public areas in which smoking is allowed.
The announcement was made in public advertisements in Arabic-language newspapers as part of a "Youth Without Tobacco" campaign.
A spokesman for Dubai municipality told AFP that cigarette vendors and managers of public places such as cafes and restaurants have been instructed to ask clients for proof of identity even to smoke water pipes.
Those breaking the law would be fined, he said without elaborating.
Before Saturday's ban the sale of cigarettes in Dubai was prohibited to anyone under 18 and smokers were not allowed to light up in public places including hotels, restaurants, cafes and offices.
The campaign was launched to coincide with World No Tobacco Day on Saturday.
The World Health Organisation said on Friday that only a total ban on all forms of tobacco advertising can stop the "constantly mutating virus" of the marketing industry and protect vulnerable young people.
Dubai, one of the seven United Arab Emirates, is a regional tourism and business hub that attracts millions of visitors each year.