US President Donald Trump is expected to order a review of a law that has long protected Twitter, Facebook and Alphabet's Google from being responsible for the material posted by their users, according to a draft executive order and a source familiar with the situation.

News of the order comes after Trump threatened to shut down websites he accused of stifling conservative voices following a dispute with Twitter after the company decided to tag Trump's tweets about unsubstantiated claims of fraud in mail-in voting with a warning prompting readers to fact-check the posts.

The order, a draft copy of which was seen by Reuters, could change before it is finalised. On Wednesday, officials said Trump will sign an executive order on...