Nigeria has arrested 200 people, mostly Chadian "mercenaries," after last week's attacks in the north, a police source said Thursday, as pressure mounts on the security forces to stem the violence.
Coordinated gun and bomb attacks in the northern city of Kano last Friday killed at least 185 people, the deadliest ever assault claimed by the shadowy Islamist sect Boko Haram.
They have been blamed for scores of other attacks across northern Nigeria.
"Many arrests have been made since the attacks," the police source said on condition of anonymity.
"We have arrested around 200 attackers and 80 percent of them are Chadians. They came in as mercenaries."
There were indications the Chadians had been paid to participate in the recent attacks attributed to Boko Haram, the source added.
Nigerian security forces have long suspected Boko Haram of smuggling arms into the country through the porous northeastern border with Chad and Niger.
A UN report on regional security released on Wednesday said there was evidence suggesting the Nigerian group had Chadian members who had received training from Al-Qaeda's north Africa affiliate.
The African Union's counter-terrorism chief Francisco Caetano Jose Madeira also warned on Tuesday that the Nigerian group may be trying expand its activities deep into Central Africa.
While some have been eager to emphasise Boko Haram's external ties, others say Boko Haram is a problem born and bred in Nigeria.
Nigerian authorities have come under immense pressure over the spiralling violence blamed on the Islamists and have in the past been accused of rounding up innocent civilians in response to attacks.
"Following previous attacks by Boko Haram, the security forces have often resorted to dragnet arrests, rather than arresting people on the basis of a reasonable suspicion that they committed an offence," Amnesty International said earlier this week.
The police faced intense criticism after suspected Boko Haram member Kabiru Sokoto, linked to a Christmas attack, escaped police custody last week in mysterious circumstances.
Nigerian President Goodluck Jonathan on Wednesday fired the country's police chief and six of his deputies.
It was the first step in a complete overhaul of the force that was suffering from a "collapse in public confidence," a presidential statement said.
The police source said on Thursday that suspected members of Boko Haram had reached out to the police for potential dialogue, with the emir of Kano as mediator. The emir is the most important traditional Muslim leader in Kano.
"They said they want the emir to mediate in the dialogue they proposed," the source said.
The group, which initially said it was fighting for the creation of an Islamic state in deeply impoverished northern Nigeria, launched an uprising in 2009 that was put down by a brutal military assault.
Boko Haram went dormant for more than a year before re-emerging with attacks that have become increasingly sophisticated.
It is now believed to have a number of factions with differing aims, including some with political links and a hard-core Islamist cell.