Social network blamed for contributing to anti-Muslim riots that left three people dead.

The Sri Lankan government has accused Facebook of failing to control rampant hate speech that it says contributed to anti-Muslim riots last week that left three people dead and the country under a state of emergency.

As mobs of hardline Buddhists rioted and lit fires in towns in the central district of Kandy, Facebook, WhatsApp and several other platforms were blocked across the country.

Harin Fernando, the telecommunications minister, said the government had taken the unprecedented step in response to fears that widely circulated videos claiming to show mosques and Buddhist temples being torched would ignite further violence.

“This whole country could have been burning in hours,” Fernando told the Guardian. “Hate speech is not being controlled by these organisations and it has become a critical issue globally.”

On Thursday Fernando, along with the Sri Lankan prime minister, Ranil Wickremesinghe, and communications officials, will meet a Facebook team that has flown to Colombo. The Sri Lankans will demand a new, faster system for taking down posts flagged as a national security risk by agencies in the country.

“Facebook is not reacting as fast as we have wanted it to react,” Fernando said. “In the past it has taken various number of days to review [flagged posts] or even to take down the pages.”

On Tuesday he highlighted a tweet from a user who claimed to have reported a Facebook post in the Sinhala language that read “Kill all Muslims, don’t even let an infant of the dogs escape.”

The user claimed he received a reply six days later saying the post did not contravene a specific Facebook community standard.

The extremist leader Amith Weerasinghe, who was arrested last week in Kandy after being accused of helping to instigate the violence, had amassed nearly 150,000 followers on his Facebook page before it was taken down last week.

Posts by other extremists that remain online include calls for Buddhist rioters to “hit them [Muslims] as hard as you can”, while another, by an activist who was arrested last November for targeting Rohingya refugees, promises groups will be going “from town to town to safeguard the future of the unborn Sinhala race”.

Questions are being raised across south Asia about the capacity and responsibility of platforms such as Facebook to monitor how they are being used in a region with tens of millions of users who post in dozens of languages and hundreds of dialects.

On Tuesday United Nations investigators said Facebook had played a “determining role” in violence against Rohingya Muslims that the US government has labelled ethnic cleansing.

“I’m afraid that Facebook has now turned into a beast, and not what it originally intended,” said the UN investigator Yanghee Lee.

Last year the Guardian revealed that the platform was accused in India of repeatedly failing to take down posts advertising rape videos and discussing child sexual abuse – claims that led the Indian supreme court to order Facebook, Google and others to overhaul the way they handled sexual abuse material.

Facebook said in a statement that the number of people working to monitor content on the platform had doubled to 14,000 in the past year and included Sinhala speakers.

“In response to the situation in Sri Lanka, we have increased our local language capabilities [and] established communications with government and non-governmental organisations to support efforts to identify and remove such content,” it said.

Facebook has more than 6 million users in Sri Lanka, the number of accounts having doubled since 2015, Fernando said. Both Facebook and WhatsApp remain restricted but the Guardian understands the block on the latter could be lifted by Wednesday evening.

“We are concerned with the way access to the internet is being restricted and depriving people of important connections and expression, and we hope that access will be restored soon,” Facebook said in its statement.

Sanjana Hattotuwa, an analyst at the Centre for Policy Alternatives in Colombo, said the government had been late in waking up to a problem many had been warning about for years.

“Many of these individuals have been operating with complete impunity, spewing hate and inciting violence, so it’s quite surprising to me that the government has finally woken up to it only after the riots,” he said.

South Asia was not the only region grappling with the rapid spread of social media, he said, “but I think in countries like ours, where there is a history of communal faultlines, political unrest, racial tensions and identity conflict, it serves to seep into those cracks.”

Sri Lanka had high literacy rates but poor information literacy, he added, making the problem more acute. “It means the population can read and write but tends to immediately believe and uncritically respond to that which they see on social media,” he said.