Beijing, Aug 11 (IANS): China's largest social media platforms -- Weibo, WeChat and Baidu Tieba -- are under investigation for alleged violations of cyber security laws, the country's internet watchdog announced on Friday.

The Office for Cyberspace Administration said the three platforms had failed to monitor content on their sites, reports the BBC.

It said people had been using the platforms to spread terrorism-related material, rumours and obscenities.

The breaches "jeopardised national security", the administration said.

Weibo, WeChat and Baidu Tieba are among the most powerful social media platforms in the world, each attracting hundreds of millions of users in China.

Last month 60 popular celebrity gossip sites were closed overnight for corrupting "core socialist values", and a new regulation released in May requires all online news portals to be managed by Communist Party sanctioned editorial staff, according to the Cyberspace Administration.

The authorities in China heavily censor the internet, routinely blocking content or search terms and removing posts they consider sensitive, the BBC reported.

They also block foreign social media sites and apps, including Facebook, Instagram and Twitter.

Search engines like Google are blocked, and access to many foreign media outlets is restricted too.