Nigeria's state security service (SSS) said on Monday it had arrested more than 100 suspected members of radical Islamist sect Boko Haram and had foiled a spate of attempted bombings in the past month and a half.
Guerrilla attacks on police stations and assassinations by gunmen on motorbikes have killed more than 150 people since the start of the year in the remote northeastern state of Borno. Boko Haram has claimed responsibility for much of the violence.
Insecurity in parts of northern Nigeria has rapidly replaced militant attacks on oil infrastructure hundreds of kilometres away in the southern Niger Delta as the main security risk in Africa's most populous nation in recent months.
"Successful security operations have led to the arrest of some identified key cell commanders and members of the dissident group in Bauchi, Borno, Kaduna, Kano, Yobe and Adamawa," the SSS said in a statement, referring to six northern states.
The sect said it was behind a car bomb last month outside the national police headquarters in the capital Abuja and there are fears that it will increasingly trying to operate beyond its home region if not brought under control.
The SSS said some of the suspects were working with the security agencies and would not be prosecuted.
"President Goodluck Jonathan has decided to use the carrot and stick approach with the suspects," the statement said.
Critics have accused Nigeria's security agencies of failing to act decisively enough to prevent bombings and shooting by Boko Haram, which has been responsible for almost daily acts of violence in and around Borno's state capital Maiduguri.
Boko Haram says it wants a wider application of sharia Islamic law across the north but its ideology is not widely shared by the majority of the region's Muslim population, the largest in sub-Saharan Africa.
Poverty and unemployment in the arid region bordering Niger, Chad and Cameroon have helped it build a cult-like anti-government following.
The SSS said its agents had uncovered or demobilised at least 12 improvised explosive devices since late May, mostly in Kaduna state, and urged the public to be on alert.
Jonathan, who was sworn in for his first full term in office in late May, has voiced support for dialogue but the group has said it will only negotiate if demands including the resignation of the Borno state government are met.