Facebook has violated Vietnam's new cybersecurity law by allowing users to post anti-government comments on the platform, state media said today, days after the controversial legislation took effect in the communist-ruled country.

Despite economic reforms and increasing openness to social change, Vietnam's Communist Party retains tight media censorship and does not tolerate dissent.

"Facebook had reportedly not responded to a request to remove fanpages provoking activities against the state," the official Vietnam News Agency said, citing the Ministry of Information and Communication.

In a statement, a Facebook spokeswoman said, "We have a clear process for governments to report illegal content to us, and we review all these requests against our terms of service and local law."

She did not elaborate.

The ministry said Facebook also allowed personal accounts to upload posts containing "slanderous" content, anti-government sentiment and defamation of individuals and organisations, the agency added.

"This content had been found to seriously violate Vietnam's Law on cybersecurity" and government regulations on the management, provision and use of internet services, it quoted the ministry as saying.

Global technology companies and rights groups have earlier said the cybersecurity law, which took effect on January 1 and includes requirements for technology firms to set up local offices and store data locally, could undermine development and stifle innovation in Vietnam.

Company officials have privately expressed concerns that the new law could make it easier for the authorities to seize customer data and expose local employees to arrest.

Facebook had refused to provide information on "fraudulent accounts" to Vietnamese security agencies, the agency said in today's report.

The information ministry is also considering taxing Facebook for advertising revenue from the platform.

The report cited a market research company as saying $235 million was spent on advertising on Facebook in Vietnam in 2018, but that Facebook was ignoring its tax obligations there.

In November, Vietnam said it wanted half of social media users on domestic social networks by 2020 and plans to prevent "toxic information" on Facebook and Google.