China’s move to block YouTube has been criticized by The Centre for Democracy and Technology.

The advocacy group told the BBC: “China’s actions fail to live up to international norms.”

YouTube has been unavailable in China since Monday, although the California firm gave no details for why Chinese authorities were barring access to the popular video-sharing website.

By early Wednesday, users in China continued to encounter an error message: “Network Timeout. The server at youtube.com is taking too long to respond.”

“China’s apparent blocking of YouTube is at odds with the rule of law and the right to freedom of expression,” said CDT president Leslie Harris.

“Anytime a country limits or takes down content online , it must be forthright and specific about its actions and do so only in narrowly defined circumstances consistent with international human rights and the rule of law,” she added.

It’s not the first time users in China have been unable to access the site. Last year, authorities blocked YouTube during riots in Tibet.