Elon Musk has put his $US44-billion ($A64 billion) deal for Twitter Inc temporarily on hold, citing pending details in support of the calculation that spam and fake accounts indeed represent less than 5 per cent of users.

Shares of the social media company fell 17.7 per cent to $US37.10 in premarket trading, their lowest level since Musk disclosed his stake in the company in early April and subsequently made a “best and final” offer to take it private for $US54.20 per share.

The implied probability of the deal closing at the agreed price fell below 50 per cent for the first time on Tuesday, when Twitter shares dropped below $US46.75.

Twitter had earlier this month estimated that false or spam accounts represented fewer than 5 per cent of its monetisable daily active users during the first quarter, when it recorded 229 million users who were served advertising.

“Twitter deal temporarily on hold pending details supporting calculation that spam/fake accounts do indeed represent less than 5 per cent of users,” Musk tweeted on Friday.

Musk, the world’s richest man and a self-proclaimed free speech absolutist, had said that one of his priorities would be to remove “spam bots” from the platform.

Twitter did not immediately respond to a request for comment. Musk’s representatives or his company Tesla Inc were not immediately available for a comment.

The social media company had said it faced several risks until the deal with Musk is closed, including whether advertisers would continue to spend on Twitter amid “potential uncertainty regarding future plans and strategy.”

Musk has been critical of Twitter’s moderation policy. He has said he wants Twitter’s algorithm to prioritise tweets to be public and was against too much power on the service to corporations that advertise.

Earlier this week, he said he would reverse Twitter’s ban on former US President Donald Trump when he buys the social media platform, signaling his intention to cut moderation of the site.