Iran restored access to Facebook yesterday after a block on the social networking website last week generated accusations that the government was trying to muzzle one of the main presidential campaign tools of the reformist opposition.

Facebook was cut off on Saturday, depriving challengers to President Mahmoud Ahmadinejad of a critical means of reaching out for the youth vote in the 12 June election.

The main pro-reform candidate, Mir Hossein Mousavi, is seeking a strong turnout from young voters and has used Facebook to try to mobilise support.

Authorities have not directly commented on the Facebook outage and the reason for its return was not immediately clear. It is not known whether the renewed access is permanent. In the past, Iranian authorities have restored then reimposed blocks on websites.

Iranian authorities often block specific sites and blogs considered critical of the Islamic regime. Critics said the shutdown of Facebook forced Iranians to rely on the government for information, depriving the election debate of important independent voices.

More than half of Iranians were born after the 1979 Islamic revolution and young voters make up a huge bloc – which helped the former reformist president, Mohammad Khatami, to back-to-back victories in 1997 and 2001. But the youth vote failed to rally strongly behind Ahmadinejad's opponent, Akbar Hashemi Rafsanjani, four years ago.

Young voters are now strongly courted by Mousavi as the possible swing factor.

An aide to Mousavi said over the weekend that the Facebook block was a reaction to a major pro-Mousavi rally on Saturday in a Tehran sports stadium that included an appearance by Khatami and many young people waving green banners and scarves – the symbolic colour of the Mousavi campaign.