Electric jammers have been placed inside the Ecuadorian embassy in London to prevent WikiLeaks founder Julian Assange having access to the internet or social media, sources say.
The Ecuadorian government took the measure on Tuesday evening, stopping Mr Assange from tweeting, using the internet or phone.
He has also been refused any visitors to the embassy, where he has been living since June 2012, believing he will be extradited to the United States for questioning over the activities of WikiLeaks if he leaves.
The measures follow the publication of an article in the Ecuadorian press concerning Mr Assange's tweets about the arrest of former Catalan president Carles Puigdemont in Germany earlier this week.
In a phone call to Mr Assange's lawyer on Tuesday, an adviser to Ecuadorian foreign minister Maria Fernanda Espinosa said the WikiLeaks founder must stop tweeting about the Catalan issue.
His lawyer was told that a decision had been taken to isolate Mr Assange by preventing him from communicating with the outside world, and that this was "by order of the president", say sources.
The Ecuador government said in a statement: "The government of Ecuador has suspended the systems that allow Julian Assange to communicate to the outside of the Ecuador embassy in London.
"The measure was adopted due to Assange not complying with a written promise which he made with the government in late 2017, by which he was obliged not to send messages which entailed interference in relation to other states."
WikiLeaks sources said there was no such agreement.
Former Greek minister Yanis Varoufakis and musician Brian Eno said in a statement: "Only extraordinary pressure from the US and the Spanish governments can explain why Ecuador's authorities should have taken such appalling steps in isolating Julian."
They added that the Ecuador government had only recently granted Mr Assange citizenship, saying it must have been "leaned on mercilessly" to stop attempting to provide a diplomatic route to safety and even drive the WikiLeaks founder out of the embassy.
"Clearly, Ecuador's government has been subjected to bullying over its decision to grant Julian asylum, support and ultimately, diplomatic status," they said.
Ecuador briefly suspended Mr Assange's internet connection in 2016 during the US presidential election. Thousands of people have signed a petition calling on the government of Ecuador to reverse its decision.