Ecuador’s government said Wednesday that it had suspended internet access for Julian Assange, the WikiLeaks founder who since 2012 has lived in Ecuador’s Embassy in London, out of concern that he was harming its relationships with Britain and other European nations.

The decision set off a furious reaction from some Assange supporters. One of them, Kim Dotcom, an online renegade who founded a file-sharing site, urged supporters to gather outside the embassy in protest. The filmmaker Oliver Stone wrote on Twitter: “Free Julian Assange! Restore his internet connection!”

Ecuador’s government granted Mr. Assange citizenship in January, the latest step in a longstanding diplomatic standoff. But it said it had suspended Mr. Assange’s online communications on Tuesday because he had imperiled “the good relations that the country maintains with the United Kingdom, with the rest of the states of the European Union, and other nations” through his social-media messages.

The government did not provide specifics, but some speculated that the decision might have been related to the Western nations’ coordinated actions against Russia after the poisoning of a former Russian spy in Britain. In a series of Twitter posts this week, Mr. Assange was critical of Western nations’ expulsions of Russian diplomats.