This article is more than 11 years old

This article is more than 11 years old

The BBC claimed today that Iran had widened electronic jamming of its services, as the country's Revolutionary Guard ordered domestic websites and blogs to remove any material that might "create tension" amid post-election unrest.

Both the BBC's World News and Persian TV channels are now being jammed by "ground-based interference" in what one senior corporation insider told MediaGuardian.co.uk was akin to "electronic warfare".

Iranian authorities also blocked access to Yahoo Messenger early today as the country intensified its crackdown on all means of communication following Friday's controversial presidential poll.

The BBC's Persian website has also been blocked by filters, although the corporation said people were finding a way to unblock them manually and that use of the site had been "massive". It was receiving five videos a minute from people within Iran.

Iran's Revolutionary Guard, an elite body answering to the supreme leader Ayatollah Ali Khamenei, said through the state news service that Iranian websites and bloggers must remove any materials that "create tension", or else they would face legal action.

This is the first public statement from what is the country's most powerful military force since the crisis erupted.

Iranian reformist websites, as well as blogs and Western social media sites such as Facebook and Twitter, have been vital conduits for Iranians to inform the world about protests over the bitterly contested declaration of election victory for the hardline president, Mahmoud Ahmadinejad.

At least 20 websites affiliated to the defeated reformist candidate, Mir Hussein Mousavi, have been blocked, although some users can still update their profiles by using proxy sites.

"Before this we could bypass filtering by using proxy websites, the links for which were distributed daily among friends by email. But now the Iranian communication ministry has also begun to tackle proxy websites too," one Iranian student said.

"But there is still a small number of people who update their Facebook and Twitter profiles by using special anti-filtering programmes installed on their PC rather than regular proxy websites. The problem is that many people don't know how to use this software."

Yahoo Messenger had played an important role since Friday, when the Iranian government began to block Iran's mobile phone network and satellite TV channels.

"Yahoo Messenger was one of the most important means that Iranians could still distribute information after the government filtered Facebook and Twitter," an Iranian graduate said.

"In the early morning I couldn't log into my Yahoo Messenger account. First I thought that's because of the government clampdowns on the internet but then I found that I have access to other websites but not my Messenger.

"The internet has a very important social function in Iran in comparison to Europe and other countries. We are one of the top 10 world's active blogging communities because of the level of censorship inside the country and now the government is cracking down on the internet as well."

An Iranian blogger added: "Iran's blogging community has been very quiet this week – mostly because they are afraid of being arrested. The government has already filtered thousands of websites and blogs since Friday's election."

The Iranian government barred foreign media yesterday from leaving their offices to report on the street protests.

Iran's opposition announced a third day of street demonstrations today.

The violence has left at least seven people dead, according to Iran's state media.

In an attempt to placate the opposition, the main electoral authority said yesterday it was prepared to conduct a limited recount of ballots at sites where candidates claim irregularities.

But the announcement did not satisfy Mousavi, who has called the election an "astonishing charade" and demanded it be cancelled and held again.

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