Iran's government has gone to some considerable lengths lately to muzzle the internet within the country's borders. Not content with only blocking Google sites and encrypted search merely once in February, the government blocked SSL connections as well as many social networking sites a second time last month ahead of the country's parliamentary elections at the beginning of March.
This month, the Irani government is suspected of a "sophisticated cyberattack" on the BBC, likely a denial-of-service attack, that coincided with the country's attempt to jam the satellite feed of the news service into Iran. In a planned speechto the Royal Television Society, Director General of the BBC Mark Thompson, while avoiding saying too much about the attack, will explain that "on the day of the cyber-attack there had also been an attempt to disrupt the Persian Service's London phone-lines by the use of multiple automatic calls."
Cutting off service of the BBC's Persian-language services isn't entirely out of the scope of possibility for the Iran's government, which has been open the drive to create about its own national internet. The annual "Enemies of the Internet" report from Reporters Without Borders cited several other attempts by Iranian authorities to undermine the freedom of the internet, such as not outright shutting down the speed of the internet but rather slowing it down to the point of ineffectiveness. Iran also maintains a formidable "cyber army" capable of carrying out cyberattacks as well as policing the internet for dissidents. Also, Iran is not shy to throw people into prison based on their activities on the internet.
At the time of writing this, Iran couldn't be reached for a statement (i.e., no Google searches turned up comments from Iranian authorities).
Awkwardly, the spokeswoman for BBC couldn't provide further comment to the BBC regarding the attack.