A Syrian war monitoring group and Kurdish activists say a surprise attack in northeastern Syria carried out by the Islamic State group has killed at least 22 people, including displaced civilians.

They say the attack took place early on Tuesday after militants sneaked into the village of Rajm Sleibi, which houses a temporary displaced camp for people fleeing IS-held areas in Syria and Iraq.

The Britain-based Syrian Observatory for Human Rights says the attack included suicide bombers and heavy clashes with Kurdish-dominated U.S.-backed rebels who are fighting IS in Syria. The Observatory put the death toll at 24 killed.

A Kurdish activist put the death toll at 22, saying the victims were mostly women and children displaced from the conflict. He spoke on condition of anonymity fearing for his safety.