“Stakes are (Ukraine).”
Mr Musk tagged the Kremlin in a follow-up tweet.
“Do you agree to this fight?” he asked in Russian.
Mr Musk’s challenge to Mr Putin is one of several posts he has shared on the war in Ukraine.
A video shared on March 5 showed him speaking directly with Ukrainian President Volodymyr Zelensky.
The same day, he tweeted: “Hold strong Ukraine.”
He added: “And also my sympathies to the great people of Russia, who do not want this.”
Following Russia’s invasion on February 24, Mr Musk gave Ukraine access to SpaceX’s satellite-internet system Starlink – a system of some 2,000 satellites designed to bring web access to underserved areas of the world.
Mr Zelensky thanked Mr Musk for that support, tweeting: “I’m grateful to him for supporting Ukraine with words and deeds.”