The block on social media including Facebook and its WhatsApp and Instagram services was announced by the government's official news portal, which cited the spread of "false news reports" online. The NetBlocks observatory said it detected an intentional blackout of the popular platforms as well as YouTube, Snapchat and Viber. Twitter appeared unaffected.
Officials likely feared that the spread of inflammatory content could provoke more bloodshed in Sri Lanka, a Buddhist-majority island nation that has large Hindu, Muslim and Christian minorities and a long history of ethnic and sectarian conflict. At least 290 people were killed in the bombings.
Ivan Sigal, head of the internet and journalism advocacy organization Global Voices, said the country's rapid action was a "telling moment." "A few years ago we'd be using these platforms to help each other and coordinating assistance. Now we view them as a threat," he wrote on Twitter.
"If I were Facebook and WhatsApp I'd take a moment to ask myself where I'd gone wrong," he said. "Cannot think of a clearer signal for lack of platform trust." It wasn't the first time Sri Lanka has blocked social media. The government imposed a weeklong ban in March 2018 because of concerns that WhatsApp and other platforms were being used to fan anti-Muslim violence in the country's central region.
Facebook is increasingly in the crosshairs of regulators, rights groups and the public as it tries to balance what CEO Mark Zuckerberg has called "giving people a voice" and demands for censorship of hate speech and other harmful content posted on its flagship site as well as on Instagram and WhatsApp.
It faced intense criticism after the right-wing extremist who attacked two mosques in Christchurch, New Zealand, last month, killing 50 people, livestreamed the massacre on Facebook. The U.N. in a report last year blamed the social media company for the spread of hate speech in Myanmar that dehumanized Rohingya Muslims and contributed to persecution that caused hundreds of thousands to flee the country.
In the past, blocking social media would have been seen as "outrageous censorship," Sigal said, highlighting the shift in attitude toward social media sites. "Now we think of it as essential duty of care, to protect ourselves from threat."
Sri Lanka's defense ministry said the shutdown would extend until the government wraps up its investigation into the bomb blasts. Sri Lanka's U.N. ambassador, Amrith Rohan Perera, said in a statement Monday that the blocks aim "to prevent speculative and mischievous attempts to spread rumors." He also cautioned expatriates to use social media responsibly to support one another but not to inadvertently spread "panic and mistrust."
NetBlocks, however, said post-attack blackouts can be ineffective. "What we've seen is that when social media is shut down, it creates a vacuum of information that's readily exploited by other parties," said Alp Toker, executive director of the London-based group. "It can add to the sense of fear and can cause panic."
"That's going to be a problem for people trying to communicate with friends and family," Toker said. Some internet users are circumventing the social media blocks by using a virtual private network, which masks the location of a computer, Toker said.
An analysis by Sri Lankan researcher and author Yudhanjaya Wijeratne of thousands of Facebook posts made during last year's ban found that many Sri Lankans simply found ways around it. Wijeratne has recommended narrower and more "technically challenging" approaches to curbing hate speech, such as better detection and strengthening local laws. He said by email Monday that the government uses Facebook as a "convenient scapegoat" but that the platform, in the time before it was cut off Sunday, was one of the most useful instruments to check in on family and friends and offer aid.
Facebook said it was aware of the Sri Lankan government's temporary blocking of social media platforms. "People rely on our services to communicate with their loved ones and we are committed to maintaining our services and helping the community and the country during this tragic time," it said.
At least 290 people died and 500 were injured in nine bomb blasts Sunday in churches and hotels. Sri Lankan officials attributed the attacks to seven suicide bombers from a local militant Muslim group.
__ Associated Press reporter Jennifer Peltz contributed to this report.