Attacks blamed on Islamist group Boko Haram followed by a heavy military crackdown have killed up to 100 people in the north of Nigeria, authorities and a rights group said Saturday.
Explosions and gunfire began on Thursday in the cities of Damaturu, Maiduguri and Potiskum in the country's northeast, where most of the violence blamed on Boko Haram has occurred, and continued into Friday in some areas.
Soldiers in trucks and armoured vehicles arrived in Damaturu on Friday and gave residents of the neighbourhood where violence had broken out 30 minutes to leave. The neighbourhood was later cordoned-off after residents fled.
The chief of army staff, Lt. Gen. Azubuike Ihejirika, was quoted by local media as saying soldiers killed 59 Boko Haram members in Damaturu. Shootouts had taken place over the course of the two days.
Others said the total death toll on all sides -- authorities, extremists and civilians -- could be as high as 100.
Sporadic firing could still be heard Saturday but the situation was generally calm, local residents and security officials said. Fresh gunfire also broke out in Maiduguri on Saturday night, residents said.
"From reports I have been receiving from Damaturu, up to 100 people could have been killed," a senior police source in the region told AFP, while Chidi Odinkalu, head of the Open Society Justice Initiative, gave a figure of 69 to 100.
Odinkalu expressed concern over what he said appeared to have been a disproportionate use of force by the military.
The military has been accused of killing civilians and burning their homes after previous bomb attacks attributed to Boko Haram.
A purported spokesman for Boko Haram claimed responsibility for the initial violence in the three northeastern cities, saying they were revenge for a brutal military assault against the sect in 2009.
"We are responsible for the attacks in Maiduguri, Damaturu and Potiskum. We carried out the attacks to avenge the killings of our brothers by the security forces in 2009," Abul Qaqa said.
"We will continue to wage war against the Nigerian state until we abolish the secular system and establish an Islamic state."
Medical sources and police gave varying death tolls and details of the attacks and crackdown remained unclear. Two senior police officers were said to be among the dead.
A spokesman for the governor for Yobe state, where Potiskum and Damaturu are located, said peace had been restored but authorities had declared a 7:00 pm to 7:00 am curfew until further notice.
Initial violence on Thursday in Damaturu saw suspected members of Boko Haram take to the streets, shooting and setting off explosions at random, according to one resident. Another said it was unclear whether Boko Haram members were in a shootout with police or carrying out attacks.
Police said they repelled the extremists and pushed them toward Potiskum, where gunfire and explosions were also later heard. Residents in Maiduguri reported six explosions on Thursday which sent people fleeing.
Maiduguri has borne the brunt of the violence attributed to Boko Haram, which has claimed responsibility for scores of attacks in the north as well as the August suicide bombing of UN headquarters in the capital Abuja that killed at least 24.
Damaturu was hit by coordinated attacks in early November claimed by Boko Haram which left some 150 people dead.
Boko Haram launched an uprising in 2009 that was put down by a brutal military assault which left some 800 dead as well as its mosque and headquarters in Maiduguri in ruins.
It lay low for about a year before re-emerging in 2010 with a series of assassinations. Bomb blasts have since become frequent and have grown in sophistication.
There has been intense speculation over whether Boko Haram has formed links with outside extremist groups, including Al-Qaeda's north African branch.
The group is believed to have a number of factions with varying aims.
Nigeria is Africa's most populous nation with some 160 million people, roughly divided between a mainly Muslim north and predominantly Christian south.