DAKAR, Senegal — Nigeria has blocked Twitter after the social media site deleted a tweet by President Muhammadu Buhari that threatened secessionist groups in the southeast of the country who had been responsible for attacks on government offices.

The government suspended Twitter, which is used by millions of Nigerians, on Friday night, after a government official called the microblogging platform’s presence in Nigeria “very, very suspect.”

The ministry of information posted the announcement of Twitter’s suspension — on Twitter.

Twitter users in Nigeria expressed outrage at the blocking of one of the main outlets that they have to criticize their government and try to hold it to account. Many circumvented the suspension by using virtual private networks to access the service, raising questions of how effective the ban will be.

Twitter said Saturday it was “deeply concerned” by Nigeria’s action and would work to restore access “for all those in Nigeria who rely on Twitter to communicate and connect with the world.”

Apparently incensed by defiance of the ban, Nigeria’s attorney general, Abubakar Malami, ordered prompt prosecutions of anyone found flouting it. Umar Jibrilu Gwandu, a spokesman for Malami, said Saturday in a statement reported by Nigerian news media that prosecutors had been directed to “swing into action” and “ensure the speedy prosecution of offenders without any further delay.”

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The statement did not specify how Twitter users would be identified for prosecution. Nor did it specify the punishment.

In the tweet deleted by Twitter on Wednesday, Buhari drew a connection between Nigeria’s civil war decades ago and attacks on offices of the national electoral commission by arsonists and gunmen.

Most of the attacks have been in the southeast, which declared itself the Republic of Biafra in the 1960s and fought a devastating war for secession. Buhari, who has 4.1 million followers on Twitter, was a commander on the side of the Nigerian government during the war.

Twitter worked on some cellphone carriers Saturday, according to tests conducted by Reuters.

Facebook and WhatsApp are the social networks used by most Nigerians, but the country’s intellectuals, activists and journalists tend to gravitate toward Twitter — and many were able to keep tweeting after the ban.

“Thank God for VPN” was trending on Twitter in Nigeria on Saturday, and many Nigerians took to the platform to comment that Africa’s biggest democracy was showing worrying signs of dictatorship in suppressing the right to free speech.

This article originally appeared in The New York Times.