Elon Musk has said Twitter will charge US $8 monthly to Twitter users who want a blue tick by their name indicating a verified account.

As part of changes after a US $44 billion takeover of the social media site, Musk says it was "essential to defeat spam/scam".

A blue tick mark next to a username - normally for high-profile figures - is currently free.

Critics says the move could make it harder to identify reliable sources.

Twitter's former method of verifying users for a blue tick included a short online application form, and was reserved for those whose identities were targets for impersonation, such as celebrities, politicians and journalists.

Source: BBC