Pakistani gunman Mohammed Ajmal Amir Kasab is suffering from fever and undergoing treatment in the high-security Arthur Road jail here. Dengue is suspected, authorities said on Sunday.

“He has been treated for fever for the past few days,” said an official. “A number of tests were conducted on him by doctors from the J.J. hospital but the results have been negative,” they said. Kasab was under observation and responding well to treatment.

The lone surviving terrorist of the 26/11 Mumbai attacks, who has been sentenced to death, is lodged in a bombproof cell. His mercy plea was rejected last month by the Maharashtra government, which has sent its recommendation to the President.