Musk, in a post on X, called out the premier as “Dirty Sanchez”, who was a “tyrant and traitor to the people of Spain”, adding a poop emoji.
In another post, Musk called Sanchez “the true fascist totalitarian”.
The posts were part of a series that also lashed out French authorities that carried out police raids on the social media giant’s Paris offices over alleged political interference and sexual deepfakes.
Sanchez had broached a social media ban for under-16s in November but fleshed out his idea on Tuesday in a package of five measures to be approved “starting next week”.
However, his coalition government lacks a parliamentary majority and often struggles to pass legislation.
Australia established a world first in December when it banned young teenagers from some of the world’s most popular platforms, including Facebook, Instagram and TikTok.
France and Portugal have also sought to follow suit. Spain has joined Denmark, Greece and France in leading a push for similar action across the European Union.