Iran’s internet shutdown, now in place for 36 hours as the authorities seek to quell escalating anti-government protests, represents a “new high-water mark” in terms of its sophistication and severity, say experts – and could last a long time.

As the blackout kicked in, 90% of internet traffic to Iran evaporated. International calls to the country appeared blocked and domestic mobile phones had no service, said Amir Rashidi, an Iranian digital rights expert.

This is far from the first time a country has blocked the internet for political reasons. Egypt’s Hosni Mubarak blocked the internet for six days during the 2011 Tahrir protests, and the Taliban shut down Afghanistan’s for 48 hours in September, ostensibly to curb “immorality”.

But the level of shutdown in Iran is unprecedented and in some ways far harsher than its 2019 digital blackout, which internet observers described at the time as the most “severe disconnection” they had seen anywhere.

“There is no reception on the phones. There is no antenna. It’s like you are living in the middle of nowhere, with no BTS towers,” said Rashidi.

Even Elon Musk’s Starlink satellite system, which was a lifeline for Iranians during the 2022 protests over the death of 22-year-old Mahsa Amini in police custody, was being jammed, Rashidi said, although the extent varied from one neighbourhood to another.

While Iranians across the country were suddenly cut off from the internet, Iran’s supreme leader, Ayatollah Ali Khamenei, continued to post on X. He did so at least 12 times on Friday, inveighing against Donald Trump and US action in Venezuela.

This is what makes this blackout different from previous internet blockages in Iran, said Doug Madory, an expert in internet infrastructure who studies such disruptions. It is more sweeping, but also appears to be more fine-tuned, which potentially means Tehran will be able to sustain it for longer.

Rashidi said: “There are things that are important for the government to do. If they want to put out their propaganda they need to have access to Telegram, they need to have access to Twitter, they need to access Instagram.”

Alluding to Mubarak’s 2011 shutdown, Madory said there were “big costs to taking everything down”.

“If you look at what happened in Egypt … the government couldn’t operate,” he said. “People really use the internet for a lot of things, and when they take it all down, nothing works.”

Based on external evidence, Madory and Rashidi believe the Iranian government has whitelisted some sites, allowing some officials and institutions to continue to access the internet.

Some of its Telegram channels appeared to be working, Rashidi said, indicating that its administrators must have internet service. The government appeared to soften the blackout briefly for university websites on Friday, then shut service down again.

All of this suggests Iran has developed more precise tools for censoring the internet. “If they end up implementing a whitelist, and it works as planned it may enable them to operate in some kind of degraded state for an extended period of time,” said Madory.

“What they’re doing is trying to set this up so that they don’t have to turn everything back on. They want just the bare necessities to be able to communicate and then shut everything else off.”

Iran has been working to upgrade its ability to censor the internet for some years, said Rashidi and Madory, trying to build a internal service similar to China’s that connects domestic users while cutting them off from the outside world.

It is not alone in trying to refine government control over the internet. India is building a government-managed messaging app to rival WhatsApp, and Russia is pushing a state-backed “super app” similar to China’s WeChat.

Iran’s national model may not yet be working, however, because sites linked to it are currently inaccessible, said Rashidi.

National internet or no, however, Madory suspects the blackout may last some time. “This might be for the long haul,” he said. “I’ve been doing this for a while and I think it’s going to be a big one.”