Alexander Borodai, self-styled former prime minister of what he declared is the Donetsk People's Republic, denied Strelkov was injured in combat with Ukrainian military troops.
The departure comes as the cities of Donetsk and Luhansk in eastern Ukraine, hotbeds of pro-Russian sentiment, are surrounded by Ukrainian forces after heavy fighting and cut off from electricity and supplies, and a convoy of over 200 trucks of what Russia terms humanitarian aid are proceeding to the Ukrainian border.
"You probably already know that he, like myself, has left his post," Borodai said on the pro-Kremlin website Life News, adding the Donetsk People's Republic "already has a new defense minister."
Borodai referred to the new minister with the nickname "Tsar." Other sources identify him as Vladimir Kononov, the BBC reported Thursday.
Strelkov's resignation comes after Alexander Zakharchenko replaced Borodai, and the Luhansk rebel chief Valery Bolotov temporarily resigned his position, earlier this week.