Nigeria has closed its northern border with Cameroon to block the movement of Boko Haram members who use the area as a launch-pad for attacks.
In a statement released on Sunday the Nigerian military claimed fighters have set up bases in sparsely populated areas of its northeastern neighbours Cameroon, Chad and Niger; and use them to flee across the border after staging attacks to avoid military pursuit.
The border closure extends from the northern Borno state, by Lake Chad, to the southern end of Adamawa state, one of three states in the northeast placed under emergency rule in May following waves of attacks by Boko Haram fighters.
|Boko Haram and the battle for Nigeria's north
The closure comes as suspected Boko Haram fighters stormed the mostly Christian village of Izghe in Borno state on Saturday, north of Adamawa, killing more than 100 people.
“What I did was completely seal off the borders, no going in, no going out,” Brigadier General Rogers Iben Nicholas, the top military commander in Adamawa told the AFP news agency.
He said the measures had been in place since Monday and had already curtailed “the influx of terrorist elements” into Nigeria.
The state of Adamawa is thought to provide key transport routes for fighters.
Despite the state of emergency, Boko Haram has continued to carry out attacks in the northeast, with more than 300 people killed this year and thousands since 2009.
On Wednesday, an attack by Boko Haram in Bama, some 60km from the Borno state capital, Maiduguri, killed 60 people.
The group's leader Abubakar Shekhau has threatened to extend the insurgency to the oil-producing south by attacking the Niger Delta region.
US Secretary of State John Kerry on Sunday condemned the wave of violence and reiterated Washington’s support for the authorities in Abuja, which includes providing “counter-terrorism assistance”.
“The people of northern Nigeria deserve to live free from violence and from terror,” the AFP news agency reported Kerry saying.
He added: “We stand with the people of Northern Nigeria in their struggle against violent extremism, and remain a committed partner of the Government of Nigeria as it works to root out Boko Haram and associated groups.”
Rise of Boko Haram
Established in 2002, Boko Haram seeks to establish an Islamic state in Nigeria, and put an end to Western influence.
The groups central belief is “Western education is sin” and prohibited in Islam.
Targeting schools and colleges, the groups campaign has resulted in thousands of parents across the region withdrawing their children from institutions where Western education is taught, fearing attacks.
Fighters launched an uprising in 2009, which left about 800 people dead and the group's Mosque and headquarters in northeastern Maiduguri in ruins.
In November the US State Department designated Boko Haram a “terrorist organisation”.