A Twitter account affiliated with the Islamic State (IS) released photos Tuesday purportedly showing the execution of captured Jordanian pilot Moaz Al Kasasbeh. The photos featured Al Kasasbeh on fire inside a cage and surrounded by armed IS militants. The authenticity of the images has not yet been confirmed. Kasaesbeh was captured in December after his F-16 fighter jet crashed in territory controlled by IS in Syria. Jordanian authorities have repeatedly demanded proof that Kasasbeh was still alive in order to proceed with negotiations with IS over the release of Sajida al Rishawi in exchange for the pilot's life. Sajida Al Rishawi, a female militant, was jailed by Jordan for her role in a 2005 suicide bomb attack that killed 60 people in the capital Amman.