Iran has reportedly gone into 'internet coma' by tightening internet controls ahead of next month's presidential election, mindful of violent protests inspired last time around over claims of fraud.
Authorities refuse to officially confirm the new restraints, but former officials and media reports have accused the Supreme Council of Cyberspace of ordering them, reports News.com.au.
According to local media, businesses, banks and even state organisations aren't being spared the widespread disruption.
Facebook, Twitter, YouTube and numerous other sites, including thousands of Western ones, have been censored in Iran since massive street demonstrations following the re-election of President Mahmoud Ahmadinejad in 2009.
Those protests were instigated online and observers say authorities are choking the internet to prevent a recurrence.
A network supervisor at a major internet service provider in Tehran said his company had been unable to address complaints about slower speeds, particularly accessing pages using the HTTPS secure communications protocol.
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The problem is not limited to slower speeds, but also affects what people can actually access.
Iran is preparing to elect a new president on June 14.