The tourist was reportedly part of a group of at least seven foreigners who climbed the mountain without registering as hikers, according to Coconuts Bali.
Mount Agung, located in Karangasem Regency in the northeast corner of Bali, is considered a dwelling place of the gods.
The Russian posted the photos that went viral on social media. Locals and tourists both condemned his act, with many calling for him to be deported. The man, who claimed he was unaware that the mountain was a sacred site, later deleted the post and issued an apology.
"I want to apologize for my actions that desecrated the sacred volcano of the local population," he wrote. "There is no excuse for my actions. The only thing that led to what happened was my personal ignorance. Ignorance of the customs of the local religion."
Bali has been stepping up law enforcement regarding foreigners, even banning them from riding motorcycles following a string of deadly accidents.