Australia's cyber watchdog has called on Twitter, which is owned by multi-billionaire Elon Musk, to explain its handling of online hate.

The country's online safety commissioner says Twitter has become the most complained about platform.

Twitter has been 28 days to respond to the regulator or face potential fines of hundreds of thousands of dollars.

Mr Musk bought the firm last year for $44bn (A$64bn; £34.5bn) and promised to protect free speech on the platform.

A legal notice was sent to Twitter demanding an explanation after one-third of all complaints received about online hate concerned the platform, Julie Inman Grant said.

That is even though Twitter has far fewer users than TikTok, Facebook and Instagram.

The company has been told to respond to the watchdog within 28 days or face penalties of up to A$700,000 (£371,570; $475,300) a day for continuing breaches.

"Twitter appears to have dropped the ball on tackling hate," Ms Inman Grant said.

"We are also aware of reports that the reinstatement of some of these previously banned accounts has emboldened extreme polarisers, peddlers of outrage and hate, including neo-Nazis both in Australia and overseas," she added.

The demand builds on a campaign by the regulator to make the social media company more accountable.

Twitter did not provide a statement on the announcement when contacted by the BBC for comment.

Earlier this month Ella Irwin, Twitter's second head of trust and safety under Mr Musk's ownership resigned. Her predecessor, Yoel Roth, left in November 2022 - a month after Mr Musk took control.

The head of trust and safety is tasked with content moderation, a topic that has come under the spotlight since the takeover.

Although Ms Irwin has not publicly said why she left Twitter, her exit came a day after Mr Musk publicly criticised a content moderation decision.

He called the decision to limit the visibility of a video over allegations of misgendering, "a mistake by many people at Twitter".

"Whether or not you agree with using someone's preferred pronouns, not doing so is at most rude and certainly breaks no laws," he wrote.

Just days later, Linda Yaccarino, the former head of advertising at NBCUniversal, took up her role as Twitter's chief executive, replacing Mr Musk.

Ms Irwin's resignation also came a week after the social media platform pulled out of the European Union's voluntary code to fight disinformation.

Since buying Twitter, Mr Musk has cut about 75% of its employees, including teams charged with tracking abuse, and changed how the company's verification process.

Meanwhile, advertisers have left in large numbers.

In her former role Ms Yaccarino is credited with helping to steer NBCUniversal through the upheaval caused by technology firms, overhauling advertising sales, and driving industry-wide debates about data gaps as audiences migrate online.