A former Nigerian presidential candidate and director of an influential online news site critical of the government has been arrested for calling for "revolution", according to security services on Sunday.
Omoyele Sowore, one of the opposition candidates in February's presidential election, on Friday called on Twitter for a march on August 5 in Abuja with a reference to "revolution".
Later Sowore, who runs the Sahara Reporters news site, said the DSS security services were at his home, but made no further comment.
On Sunday, DSS spokesman Peter Afunaya confirmed the former candidate had been detained and was in custody.
"We cannot allow any person or group to foment chaos or fan the embers of revolution," he said on Sunday.
"If someone is calling for revolution in Nigeria, it means a revolt... insurgency. He has crossed the line, threatened public safety."
Sowore is a fierce opponent of President Muhammadu Buhari, who won another four-year term in February and faces challenges including an Islamist insurgency, a fragile economy and rife corruption.
Sowore's news website has often highlighted alleged graft in the government.
In his Friday tweet he wrote: "All that is needed for a #Revolution is for the oppressed to choose a date they desire for liberty, not subjected to the approval of the oppressor. #RevolutionNow #DaysofRage #August5".
He gave no further details of what was planned for that date.
Sowore, of the African Action Congress party, had joined other the new opposition candidates such as Kingsley Moghalu, a former central bank deputy governor, and Fela Durotoye, a motivational speaker, in the run for the presidency.