White House Press Secretary Sean Spicer has resigned after six months, an official has told NBC News.

The sudden departure comes as Donald Trump transition team official Anthony Scaramucci was slated to be announced as White House communications director.

Mr Spicer often found himself answering tough questions from reporters regarding Mr Trump's campaign officials' conversations with Moscow and the president's tweets.

A White House official said Mr Scaramucci's appointment is expected to be announced on Friday. He did not immediately respond to a request from NBC News for comment.