Many supporters of reform in Iran are said to use the Facebook site
Iran has restored access to Facebook, the social networking site which had been blocked since Saturday.
Media close to reformists had suggested the site was suspended to prevent its use by backers of presidential candidate Mir Hossein Mousavi.
On Monday President Mahmoud Ahmadinejad sidestepped questions about whether the authorities had ordered the blocking ahead of the 12 June election.
He said officials had no need to shut down any sites.
Correspondents say websites like Facebook have become an important way for candidates to mobilise younger voters in Iran ahead of the election.
Facebook, which says it has 175 million users worldwide, had expressed its disappointment over the disruption.
It said the problems had come "at a time when voters are turning to the internet as a source of information about election candidates and their positions".
Mir Hossein Mousavi, a former prime minister, is seen as one of the leading challengers to the incumbent, President Ahmadinejad.
Other candidates are a former speaker of parliament, Mehdi Karroubi, and an ex-head of the Revolutionary Guards, Mohsen Rezai.