eSafety Commissioner Julie Inman Grant said disturbing content, such as video from the 2019 mosque shootings in New Zealand, continued to spread on mainstream social media platforms.

Notices have been sent to six companies -- Google, Meta, X, WhatsApp, Telegram and Reddit -- which now have 49 days to respond.

"It's no coincidence we have chosen these companies to send notices to as there is evidence that their services are exploited by terrorists and violent extremists," Inman Grant said.

"We want to know why this is and what they are doing to tackle the issue."

Australia has spearheaded efforts to hold the tech giants accountable for what their users post online, under its groundbreaking "Online Safety Act" passed in 2021.

Inman Grant, herself a former employee of the rebranded Twitter, said the legal notices would help the regulator "get a look under the hood at what they are and are not doing".

This is not the first time Australia has targeted the tech giants, issuing similar legal notices in February that asked them to address child sexual abuse content.

But Australia's efforts to enforce social media regulations have occasionally been met with indifference.

The legal notices ask the companies to "report on steps they are taking to protect Australians from terrorist and violent extremist material and activity".

Australia's eSafety Commission recently slapped X with an Aus$610,500 (US$388,000) fine for failing to demonstrate how it is combatting child sexual abuse content.

X, formerly known as Twitter, launched its own legal action in a bid to contest the fine.