YEKATERINBURG, October 22 (RIA Novosti) - Some 12 school girls were poisoned after they ate porridge laced with detergent at a school in the city of Chelyabinsk in the Urals, the local health department's press service said on Wednesday.

The incident occurred early on Wednesday during a home economics class, when two groups aged 12-13 were being taught how to cook buckwheat and rice porridge.

"One of the students decided to play a trick on her class mates by adding some detergent powder to salt," the press service said in a statement.

The pupils are currently in hospital in a satisfactory condition and are expected to be discharged in the next few days once they have completed their course of treatment.