Nigerian authorities on Thursday interrogated a man believed to be a spokesman for Islamist group Boko Haram, as security forces battle to stop a wave of attacks blamed on the extremists.
Several security sources said Wednesday that a suspect believed to be the person who goes by the alias Abul Qaqa had been arrested, but authorities have not officially confirmed his detention or his identity.
One security source said he was flown to the capital Abuja on Wednesday and was undergoing questioning there.
"He is under interrogation," the source said on condition of anonymity, declining to provide further details.
Meanwhile, the country's newly appointed police chief Mohammed D. Abubakar visited Kano, Nigeria's second-largest city which was hit by coordinated bombings and shootings on January 20 that left at least 185 people dead.
President Goodluck Jonathan, under immense pressure over the government's failure to stop attacks blamed on Boko Haram, sacked police chief Hafiz Ringim and all Ringim's deputies on January 25.
There was heavy security in Kano for Abubakar's visit, particularly around his private home and a helicopter hovered above the city.
Abubakar said he was considering sending more police to the flashpoint northern hub because the current force is "not ... enough to police Kano".
"No right-thinking human being will be happy with what has happened" in the city, Abubakar said.
The man known as Abul Qaqa has claimed to speak on behalf of Boko Haram on numerous occasions and claimed responsibility for scores of attacks, including the Kano violence, the group's deadliest ever strike.
The purported spokesman has regularly held phone conferences with journalists in the northeastern city of Maiduguri, Boko Haram's base.
Differing versions of the arrest emerged, with one source saying he had been detained in the northern city of Kaduna on Wednesday and others saying it occurred in a raid in Maiduguri on Tuesday.
"He was tracked down using state of the art tracking equipment," a source with the secret police said.
Local media reported that agents used GPS to track him and that the suspect was from the Igala ethnic group in central Kogi state.
Marilyn Ogar, a spokeswoman for the secret police, did not respond to phone calls on Thursday, but on Wednesday said she could not confirm any arrest.
"When you have an ongoing operation, a lot of people are brought in, and until you are able to put a face to a name (nothing can be confirmed)" Ogar said.
Boko Haram has carried out increasingly sophisticated attacks, mostly in Nigeria's north, that have left hundreds of people dead.
The spiralling violence has sparked deep concern in the international community and shaken the country, whose 160 million population is roughly divided between a mainly Muslim north and predominantly Christian south.
There has been intense speculation over whether Boko Haram has formed links with outside extremist groups, including Al-Qaeda's north African branch.
Analysts say the violence has been fed by deep poverty in the north, where masses of unemployed youths have little trust in government or hope for the future in a country long considered one of the world's most corrupt.
The Arewa Consultative Forum, a group of northern elites, condemned the Kano attacks in a statement this week, but called for the government to guarantee the safety of Boko Haram members who choose to participate in dialogue.
Boko Haram has mainly targeted police stations and other symbols of authority. Christians have also been killed, including in a wave of bomb blasts on Christmas day, but Muslims have been victims of attacks as well.
The group has also claimed responsibility for the August suicide bombing of UN headquarters in Abuja which killed at least 25 people.
It launched an uprising in 2009 put down by a brutal military assault that left some 800 dead. After going dormant for about a year, it re-emerged with a series of shootings and bomb blasts.