"The Zionist regime is dying," said Iran's Ayatollah Ali Khamenei in a post on X.
Israel and the US have repeatedly called for their allies to join in their recognition of the IRGC as a terrorist entity, though many countries remain hesitant to do so.
The new security chief has a background in the IRGC navy and also in conducting operations near Bandar Abbas.
The poisonings began in November in the holy Shi'ite Muslim city of Qom and spread to 25 of Iran's 31 provinces, prompting some parents to take children out of school and protest.
This decision by Iran’s supreme leader Ayatollah Ali Khamenei was announced on Sunday and was on the front page of pro-regime media.