Image copyright Getty Images Image caption Twitter has defended its decision, saying it will 'build trust'

Some of the world's biggest celebrities have lost millions of Twitter followers after the company cracked down on "locked" accounts.

US singer Katy Perry, the most-followed user on Twitter, and Lady Gaga lost about 2.5 million followers. Barack Obama went down 2.1 million.

Twitter said it had taken the decision due to its "ongoing and global effort to build trust".

It follows renewed scrutiny over fake news and users on social media.

The new measures mean that any user whose account is locked for unusual activity - such as being blocked or sending unusual volumes of Tweets - and who did not respond to a prompt to verify their identity would be excluded from Twitter follower counts.

The head of the company's legal team, Vijaya Gadde, said that most accounts would only lose around four followers as a result of the new measures.

But she warned that more popular accounts would "experience a more significant drop".

Image copyright Reuters/Getty Images Image caption Singer Katy Perry and former US President Barack Obama both lost millions of Twitter followers in a crackdown by the site

Nowhere has this been more true than with Twitter's own account on the platform, which lost 7.7 million followers.

Twitter argued that the recent move was aimed at building users' confidence and reflected the fact that follower counts are "a visible feature" on the platform.

In January, New York's chief prosecutor said the state had launched an investigation into a company, which allegedly sold millions of fake followers to social media users.