The Egyptian dissident Mohamed ElBaradei warned President Hosni Mubarak today that his regime is on its last legs, as tens of thousands of people prepared to take to the streets for a fourth day of anti-government protests.

The Nobel peace prize winner's comments to the Guardian represented his strongest intervention against the country's authoritarian government since he announced his intention to return to Egypt to join the protests. "I'm sending a message to the Guardian and to the world that Egypt is being isolated by a regime on its last legs," he said.

His words marked an escalation of the language he used on arrival in Cairo last night, when he merely urged the Mubarak government to "listen to the people" and not to use violence.

ElBaradei has been criticised by some Egyptians for the late return to his homeland, two days after the protests began – hundreds of people have already been arrested and exposed to the brutal tactics of the security services. But ElBaradei was keen to stress his solidarity with the protesters.

"There is of course a risk to my safety today, but it's a risk worth taking when you see your country in such a state you have to take risks," he said. "I will be with the people today."

In an apparent bid to scupper the protests, the Egyptian authorities have cut off almost all access to the internet from inside and outside the country. ElBaradei said the move was proof the government was in "a state of panic".

"Egypt today is in a pre-information age," he said. "The Egyptians are in solitary confinement – that's how unstable and uncomfortable the regime is. Being able to communicate is the first of our human rights and it's being taken away from us. I haven't seen this in any other country before."

He said the lack of communications could hamper organisation of the demonstrations, planned to begin after Friday prayers. "I don't know what my hopes are for today," he said. "It would be hard with the communications cut off but I think a lot of people will be turning out." Organisers of the marches – dubbed "the Friday of anger and freedom" – are defying a government ban on protests issued on Wednesday. They have been using social media to co-ordinate plans, and hope to rally even more than the tens of thousands who turned out on Tuesday in the biggest protests since 1977.

ElBaradei has already criticised the US secretary of state, Hillary Clinton, for describing the Egyptian government as stable and he stepped up his calls for the rest of the world to explicitly condemn Mubarak, who is a close ally of the US.

"The international community must understand we are being denied every human right day by day," he said. "Egypt today is one big prison. If the international community does not speak out it will have a lot of implications. We are fighting for universal values here. If the west is not going to speak out now, then when?"