The petition, which was signed by 2 million supporters, follows a report last month in the independent newspaper Novaya Gazeta which suggested that more than 100 gay men were rounded up and tortured, and at least three killed, in the ultra-conservative southern Russian region.
The activists, four of whom were Russian, were released later on Thursday and Guaiana said they were arrested for holding an unauthorised public demonstration.
"I have just been released, now I'm rushing to the hotel; I'll pack and try to leave the country as soon as possible,” he added.
Foreign Minister Angelino Alfano congratulated the Italian embassy in Moscow on an "excellent" job in securing Guaiana's release.
Earlier, Foreign Affairs Undersecretary Benedetto Della Vedova confirmed the Italian consul had visited Guaiana in detention.
The activist said he hadn’t had anything to eat or drink since being arrested and thanked Della Vedova and the Italian consul for stepping in.
Amnesty International condemned the detention of the activists, describing it as a "violation of fundamental rights".
