"We are disappointed to learn of reports that users in Iran may not have access to Facebook," the company told AFP in a statement.
One Iranian news agency reported earlier that the government had blocked access to Facebook ahead of June presidential polls, allegedly to prevent supporters of the leading opposition candidate from using the site for his campaign.
Facebook said it was investigating the reports, and expressed disappointment that the site was apparently blocked "at a time when voters are turning to the Internet as a source of information about election candidates and their positions.
"It is always a shame when countries' cultural and political concerns lead to limits being placed on the opportunity for sharing and expression that the Internet provides."
One Facebook page, dedicated to Mir Hossein Mousavi, a rival of the incumbent president Mahmoud Ahmadinejad, has more than 5,200 supporters.
Iranian state-controlled television and radio have already been the focus of debate over whether candidates will get equal treatment.
Facebook, founded in 2004 by then Harvard student Mark Zuckerberg, claims to have 175 million members worldwide.
In Iran, the service is normally available in Farsi and in English.
