Boko Haram has claimed responsibility for the Christmas Day explosions and other attacks across Nigeria [AFP]

Nigeria's state security agents say they have arrested a man they say is a self-declared spokesman for Boko Haram, who frequently made statements to the media after attacks by the radical Islamist group.

A State Secutity Services (SSS) source said on Wednesday that a man they believed to be 'Abu Qaqa', a pseudonym used by the spokesman, was being held in the northern city of Kaduna.

"We are still talking to him. Since 'Abu Qaqa' is a pseudonym for the Boko Haram spokesman, we want to be sure of who we have with us. But we have been on his trail for months now. He's been changing locations and contacts," the source told the Reuters news agency.

At least 185 people died in a co-ordinated attack blamed on Boko Haram in the northern city of Kano on January 20.

Al Jazeera's Yvonne Ndege, reporting from Abuja on Wednesday, said that while the arrest had been welcomed, questions were being raised about how credible and important his capture was.

"Abu Qaqa has been known to have given statements to journalists about the group’s aims and ambitions but the SSS will most likely interrogate him to gain intelligence that may lead to the apprehension of other Boko Haram members," she said.

"Having said that, there have been stories that there is a split in the group, and that raises questions about where he fits in in those factions

"There is no doubt today’s arrest will go a long way in restoring public confidence in President Goodluck Jonathan’s government, which has been under tremendous pressure to bring the group to book."