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By Newley Purnell and Jon Emont 

As Sri Lankan authorities scrambled amid a wave of deadly bombings across the country on Easter morning, among their first responses was to block social media, including Facebook and the popular messaging service WhatsApp.

Both services, owned by Facebook Inc., and others functioned poorly or ceased to work altogether in the hours after the attacks Sunday, according to users.

The curbs reflect growing concerns in many parts of the world about the spread false information and hate speech on social media and the use of online platforms to incite or exacerbate tensions. The government's steps also underscore their concern that social media companies cannot control harmful content themselves.

Prime Minister Ranil Wickremesinghe called on Sri Lankans to "please avoid propagating unverified reports and speculation. The government is taking immediate steps to contain this situation."

But others say that cutting off social media during a crisis limits the ability of citizens to seek assistance and confirm the safety of family and friends, while curbing the government's capability to refute rumors and disseminate emergency information.

Facebook and other digital spaces have come under sharp criticism in recent years as extremists have used them to stoke violence in the real world, including in Sri Lanka and Myanmar. A number of countries have focused attention on the gaps in social media companies' policing of online posts and are seeking to impose regulations on them.

In March last year, Sri Lanka's government blocked social media in parts of the country after rumors and anti-Muslim posts circulated unchecked as sectarian violence broke out. Facebook also has been used to stir up hatred and deadly attacks against Muslims in Myanmar.

Facebook has taken some steps to improve its ability to remove harmful content relating to the two countries and to respond faster to volatile situations. Facebook Chief Executive Mark Zuckerberg has said the company is investing heavily in efforts to police hate speech, including hiring tens of thousands of content moderators world-wide.

Still, companies like Facebook face numerous challenges, from the limits of artificial intelligence tools to uncover hate speech to religious and ethnic complexities in countries like Sri Lanka and the difficulties in moderating content in dozens of languages.

Mr. Zuckerberg has said artificial intelligence is years away from being able to manage the problem without significant human involvement.

On the flip side, social media can also be a powerful tool in combating misinformation that is sanctioned by governments. Last week, activists in Sudan credited Facebook as a key factor in helping to topple an autocratic government, as organizers used the platform to promote protests and refute comments from officials that the movement was losing momentum.

In Sri Lanka, government officials confirmed that authorities blocked access to social media as part of a broader curfew order. Economy Minister Harsha de Silva called the ban temporary in a press conference, and said access would be allowed again early Monday morning.

At least eight explosions tore through churches and international hotels in Sri Lanka on Sunday, killing at least 207 people and wounding more than 450 in what appeared to be coordinated attacks on tourists and the minority Christian community. Most of them focused on the capital.

Instagram, YouTube, Viber, Snapchat and Facebook Messenger were also among the sites blocked, according to NetBlocks, a London-based digital rights group, and other internet monitoring groups.

A Facebook spokeswoman confirmed that Facebook, WhatsApp and Instagram were blocked, among other social media platforms. Viber didn't immediately respond to a request for comment. A representative for Snapchat couldn't immediately be reached.

Twitter appeared to be unaffected, with users in Sri Lanka continuing to post tweets. A spokesman for Twitter Inc. didn't immediately respond to a request for comment.

"It's been a while since we saw a post-attack shutdown like this," said Alp Toker, NetBlocks's director. "These disruptions are extremely problematic as they limit the public's ability to seek assistance and check up on friends and family in a time of crisis."

Government officials, however, have argued that social media encourages the spread of misinformation. Several, including the country's prime minister, used Twitter to discourage people from speculating about who perpetrated the attacks or disseminating information that wasn't issued or confirmed by authorities.

Write to Newley Purnell at newley.purnell@wsj.com and Jon Emont at jonathan.emont@wsj.com

(END) Dow Jones Newswires

April 21, 2019 17:35 ET (21:35 GMT)

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