Russians posted photos of themselves in front of the flag dressed up in bright rainbow outfits and makeup, or kissing their same-sex partners.
The flag was unveiled on the day that Russians nationwide started voting on constitutional amendments that would add a clause defining marriage as a union between a man and a woman to the Constitution.
Critics say the clause would effectively prevent gay marriage from ever being legalized in Russia.
U.S. President Donald Trump banned American embassies from hanging Pride flags on official embassy flagpoles in early June, contradicting the Trump administration's official statements in support of the LGBT community for Pride month.
The U.S. Embassy wrote in a statement that "June is Pride Month and we celebrate that everyone deserves to live a life free from hatred, prejudice and persecution."
According to public polling, young Russians tend to be more tolerant of the LGBT community than older generations.
This photo shows two men kissing and holding the popular gay romance novel "What If It's Us."
"I want this reality for all of us: Support, pride, equal treatment. Honestly, I have no hope," the Instagram user who posted the photo wrote.
The flag's June 25 unveiling also marked the 42nd anniversary of the rainbow flag's first appearance at a gay pride parade in San Francisco in 1978.
Despite gradually improving opinions, gay rights continue to be a contentious topic in Russia, with one in five Russians believing that LGBT people should be “eliminated,” according to a poll conducted in April. LGBT people in Russia often face discrimination, threats and violence.