By Lanre Ola
MAIDUGURI, Nigeria (Reuters) - The Nigerian army said on Saturday it had tracked down and killed 50 members of Boko Haram, days after the Islamist sect was blamed for killing 20 villagers in raids in its northeastern stronghold.
"Troops pursued the terrorists to their camps and with air support about 50 terrorists were killed in a shoot-out," army spokesman Sagir Musa told reporters in Borno state capital Maiduguri.
"The villages have been rescued from the fangs of the insurgents. Troops are pursuing the remnants of the fleeing terrorists by blocking all possible exit routes," Musa added.
Boko Haram, which wants to impose Islamic law in northern Nigeria, and other splinter Islamist groups, are considered the biggest security threat in Nigeria, Africa's top oil exporter.
The military sometimes exaggerates its successes and plays down its own casualties and the deaths of civilians, residents of Borno and rights groups have said. Musa said the number of civilian casualties in the latest offensive was not known.
More than 160 people were killed in violence linked to Boko Haram last month - one of the bloodiest since President Goodluck Jonathan declared a state of emergency and a military crackdown in three northeastern states in May. A new army division was sent to Borno last month.
A civilian militia - often armed with no more than clubs and knives - has been operating against the Islamists in recent weeks, leading to the arrest of hundreds of them, the military says.
The vigilantes and their families have become targets and scores have been killed in revenge attacks.
Jonathan is under intense political pressure due to a split in his party and from a recently formed opposition coalition. He has been criticized for not quelling Boko Haram's insurgency, which has intensified under his leadership.
A military offensive ended Boko Haram's initial uprising in 2009, when the group's leader Mohammed Yusuf was killed in police custody, but the sect regrouped and came back stronger, launching a more committed insurgency nearly three years ago.
While Boko Haram's bomb and gun attacks on schools, churches, mosques and markets have gained it international notoriety, the group more commonly targets police, soldiers and politicians.
The sect has several factions and an ill-defined leadership structure, which has hobbled efforts to strike a peace deal.
The military said last month Boko Haram's leader Abubakar Shekau may have died in late July of wounds inflicted during a gun battle, but the report could not be independently verified.
Western governments are concerned that northern Nigeria and the wider Sahel region could become the next main springboard for international Islamist militant attacks.
Boko Haram was blamed for bombing the United Nations building in Abuja in August 2011 which killed 25 people.
(Writing by Joe Brock; Editing by Robin Pomeroy)