WikiLeaks on Monday alleged that Assange's internet access was cut Saturday after it published private speeches by Democratic presidential nominee Hillary Clinton to Goldman Sachs.
Assange has been staying at the Ecuadoran embassy in London since 2012 to evade prosecution by Sweden over a rape allegation.
In a series of tweets beginning late Monday, the anti-secrecy site said it learned from "multiple US sources" that Ecuador cut off Assange's internet connection at the behest of US Secretary of State John Kerry.
But State Department spokesman John Kirby, in a brief statement, denied that Washington had played any role in the move.
"While our concerns about WikiLeaks are longstanding, any suggestion that Secretary Kerry or the State Department were involved in shutting down WikiLeaks is false," Kirby said.
"Reports that Secretary Kerry had conversations with Ecuadorian officials about this are simply untrue. Period."
On Saturday, WikiLeaks published three private, paid speeches Clinton made to Wall Street investment giant Goldman Sachs, after she left her position as secretary of state and before launching her White House bid.
Clinton's campaign team, which has not contested the authenticity of the documents, accused WikiLeaks and the Russian government leaking them in an effort to help Donald Trump, her Republican rival for White House.
