Beirut (AFP) - The extremist Islamic State group has closed playgrounds in a Syrian city because they were being used as a meeting place for unrelated men and women, a monitor said Sunday.

"IS has shut down playgrounds in the city of Mayadeen in the eastern Deir Ezzor province... under the pretext that there was mixing between men and women bringing their children to play," said the Syrian Observatory for Human Rights.

The Observatory's sources inside the city said that the Hesbah -- IS's moral police -- had patrolled through Mayadeen's playgrounds on the first of day of Eid al-Adha, the Muslim feast of sacrifice, earlier this week.

They then proceeded to arrest several men and women "for not abiding by Islamic rules on dress".

The ultra-radical organisation has imposed its extreme interpretation of Islam in areas under its control across swathes of Syria and Iraq.

Individuals of the opposite sex are not allowed to interact if they are not married. And women -- who are to cover their whole bodies and faces -- must be accompanied by a male member of the family at all times.

In the jihadists' de facto capital of Raqa in northern Syria, three women were arrested in a playground on Sunday by IS police for "not being accompanied by men," the Observatory said.

IS has used brutal violence -- including beheading, crucifixion, and stoning -- to maintain control in the "caliphate" it declared last year.