Whistleblower Edward Snowden is urging British people to demand the resignation of U.K. Prime Minister David Cameron over the revelations in the Panama Papers.
During a series of tweets the exiled American said U.K. citizens should attend a protest outside Downing Street on Saturday.
Cameron is under fire for failing to previously disclose that he and his family had invested in an offshore investment fund run by his late father, which was exposed in this week's massive Panama Papers data dump.
In one tweet, Snowden, who now lives in Moscow, said Cameron's case was more serious than that of Iceland's former Prime Minister Sigmundur David Gunnlaugsson, who stepped down Wednesday following revelations that his wife had an offshore trust with ties to some of Iceland's bankrupt banks.
"It's up to the British people, not us. In Iceland, 10 percent of all voters were in the streets within 24 hours, and for less," Snowden tweeted Thursday.
In an earlier tweet, Snowden mocked Cameron for insisting that his family's tax affairs were not a public matter.
"Oh, now he's interested in privacy," Snowden's message said curtly.
The Cameron family tax arrangements came to light following a massive leak of documents from Panama-based law firm Mossack Fonseca.
According to the documents, Cameron's late father ran an investment vehicle which avoided paying tax in the United Kingdom by having directors hold board meetings in Switzerland and the Bahamas.
After initially refusing to divulge details on his interest in the fund, the U.K. leader revealed to ITV news Thursday that he and his wife had previously held a stake in the offshore trust.
Cameron said he sold the shares before he entering Number 10 in 2010 and had paid all UK taxes due on profits from the £30,000 sale.
When asked by ITV whether his recent £300,000 inheritance from his father had originally benefited from offshore tax arrangements, Cameron said he could not be sure.
"I obviously can't point to the source of every bit of money and dad's not around for me to ask the questions now," he said.