They were reportedly checking their home in the town when the blast occurred.

"A member from the “Islamic State” and his sister were killed by a landmine explosion, it was planted by the organization earlier near the bank of the Euphrates in the town of al-Jninah in the western countryside of Deir Ezzor in order to prevent the smuggling of food into regime forces controlled areas in Deir Ezzor, the organization’s member and his sister were checking their home in the town when the landmine exploded under them," the Syrian Observatory for Human Rights said on its website.