Nigeria on Saturday introduced a decree suspending Twitter indefinitely, drawing sharp criticism from rights groups and diplomats.
The development took place two days after the social media giant deleted a tweet from the Nigerian president, saying he had violated Twitter's rules and regulations.
International human rights groups and diplomats have condemned the move, which followed previous attempts by the government of Africa's most populous country to regulate social media.
"The Federal Government has suspended, indefinitely, the operations of the microblogging and social networking service, Twitter, in Nigeria," ministry of information and culture spokesman Segun Adeyemi said in a statement Friday.
The Association of Licensed Telecoms Operators of Nigeria (ALTON) confirmed its members had received formal instructions from the Nigerian Communications Commission (NCC), the industry regulator to suspend access to Twitter.
It said in a statement that members had "acted in compliance".
"Network data show that access to the Twitter platform and backend servers is now restricted on leading networks MTN, Globacom, Airtel and 9mobile," the London-based internet monitor Netblocks wrote on its website Saturday.
Another group representing local telecoms, the Association of Telecommunications Companies of Nigeria (ATCON) said it was working with the authorities "to ensure a speedy resolution of the suspension."
"While the Association and its member companies understand the position of the federal government, the reasons for the directive, and have complied with the directive, it is pertinent that the issue is resolved soon in the interest of all," ATCON president Ikechukwu Nnamani said.
'Repressive action'
Amnesty International on Friday condemned the moved, calling on Nigeria to "immediately reverse the unlawful suspension".
"This repressive action is a clear attempt to censor dissent & stifle the civic space," Human Rights Watch researcher Anietie Ewang said.
Twitter said that the move was "deeply concerning".
"We're investigating and will provide updates when we know more," the company said in a statement.
Twitter on Wednesday deleted a remark on the president's account after he referred to the country's civil war four decades ago in a warning about recent unrest.
The 78-year-old president, a former general, referred to "those misbehaving" in recent violence in the southeast, where officials blame a proscribed separatist group IPOB for attacks on police and election offices.
"Those of us in the fields for 30 months, who went through the war, will treat them in the language they understand," the president had posted on Twitter.
The presidency denied late on Saturday that the Twitter suspension was a response to the removal of that post.
"There has been a litany of problems with the social media platform in Nigeria, where misinformation and fake news spread through it have had real world violent consequences," a presidency spokesman Garba Shehu said in a statement.
Shehu said the removal of Buhari's tweet was "disappointing" and said "major tech companies must be alive to their responsibilities."
"Twitter does not seem to appreciate the national trauma of our country's civil war. This government shall not allow a recurrence of that tragedy," Shehu added.
Reacting to suspension of Twitter in the country, the UK's deputy high commissioner in Nigeria Gill Atkinson said "any action taken by government must be measured, proportionate and not suppress basic freedoms".
"VPN app" was the second most searched trend Saturday on Google in Nigeria, as virtual private networks can enable Twitter users to bypass the ban.
Nigeria warned however that it would prosecute violators.
"Attorney General of the Federation and Minister of Justice, Abubakar Malami, has directed for immediate prosecution of offenders of the Federal Government ban on Twitter operations in Nigeria," spokesman Umar Jibrilu Gwandu said.
Twitter has millions of users in Nigeria where the median age is 18, and has played a role in public discourse with hashtags #BringBackOurGirls, after Boko Haram kidnapped 276 schoolgirls in 2014, and #EndSARS, during anti-police brutality protests last year.
Several countries including China and Turkey have come under fire for putting restrictions on social media platforms such as Twitter.
In February Twitter condemned Myanmar for blocking access to its platform as part of a crackdown on social media, days after a coup that saw Aung San Suu Kyi and other civilian leaders jailed.
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