IS published graphic photos of the bodies of the hostages, Chinese national Fan Jinghui and Ole-Johan Grimsgaard-Ofstad of Norway, in its English-language Dabiq magazine.
It was unclear when, where, or how they were killed, but their heads were bloodied by apparent gunshot wounds.
"These crimes once again demonstrate the brutality of ISIL, which is responsible for thousands of crimes and abuses against people from all faiths, ethnicities and nationalities, and without regard to any basic value of humanity," said a statement from the 15-member council.