“Police forces arrested 11 girls and 21 boys on Thursday night for drinking alcoholic drinks and being half-naked,” the commander of Teheran province’s security police Nader Sarkari was quoted as saying.

He said the raid came after a tip-off and that the students were celebrating after one of them had won a medal in an international competition.

Less than two months ago, Iranian police arrested 20 young people in a raid on a party in the city of Karaj, which was also the site of an illegal rock concert last week when 230 were detained.

Iran is experiencing one of its tightest moral crackdowns in years. The campaign has already seen thousands of women warned by police for dressing in a way that is deemed to be unIslamic.

Mixed-sex parties are illegal in Iran. It is also forbidden to consume alcohol in public or private and attend gatherings with improperly clad members of the opposite sex. Dancing to Western music is frowned upon as well.

Iran’s overall police chief Esmaeel Ahmadi Moghaddam has said that the moral crackdown -- dubbed a drive to “elevate security in society” -- would continue because it had proved popular with the public.