The sister of a man suspected of being a masked, British-accented militant in an Islamic State propaganda video says she still holds out hope that it is not him.

Konika Dhar told Parliament's Home Affairs Committee Tuesday that she found it hard to recognize the masked militant as her brother Siddhartha Dhar, despite vocal similarities. She said that "as far as I'm concerned, I grew up with a different person."

British media have reported that the man in the video, in which five purported spies were shot dead, might be Dhar, a Muslim convert also known as Abu Rumaysah.

His sister said the family was in the dark about how he developed increasingly radical views, but felt guilt about failing to stop his transformation.