Elon Musk is attempting to drop his $US44 billion ($64 billion) bid to buy Twitter. 

The Tesla CEO has sent a letter to Twitter's board saying he is terminating the planned acquisition.

However, Twitter could take legal action to ensure the deal goes ahead.

Shares of Twitter fell 5 per cent after the announcement. 

Mr Musk said Twitter had “not complied with its contractual obligations” surrounding the deal, as it had not given Mr Musk enough information to “make an independent assessment of the prevalence of fake or spam accounts on Twitter's platform”.

Twitter executives have instituted a hiring freeze since Mr Musk’s offer was made in March. The company has also been laying off staff, most recently part of its talent acquisition team.