Nigeria began a military campaign today to force Islamist militants out of bases in its border areas after President Goodluck Jonathan declared a state of emergency in the country’s north east.
Nigerian troops moved into the region in large numbers, part of a plan to fight an insurgency by the Boko Haram Islamist group that has seized control of significant parts of the region.
"The operations, which will involve massive deployment of men and resources, are aimed at asserting the nation's territorial integrity and enhancing the security of ... all territories within Nigeria's borders," a statement from Defence Headquarters said.
Army trucks carrying soldiers entered Yola and Maiduguri after President Jonathan declared the emergency last nigth in three states: Borno, Adamawa and Yobe.
The declaration followed attacks by Boko Haram militants.
The insurgency has cost thousands of lives and destabilised Africa's top energy producing nation since it began in 2009.
Boko Haram has targeted the security forces, Christian worshippers and politicians in Nigeria's mainly Muslim north.
The troop deployment is likely to placate some of Mr Jonathan's critics, who had accused him of not facing up to the gravity of the crisis.
However, some northern politicians have already voiced concerns over the increasing tensions.
Military officials in the northeast and at headquarters in the capital Abuja were not immediately available for comment.
President Jonathan announced the move in a televised address.
His orders followed growing evidence that a better equipped, better armed Boko Haram now controls territory around Lake Chad, where local officials have fled.
"What we are facing is ... a rebellion and insurgency by terrorist groups which pose a very serious threat to ... territorial integrity," Mr Jonathan said in the address.
"Already, some northern parts of Borno state have been taken over by groups whose allegiance is to different flags and ideologies."
Officials say militants control at least ten local government districts of Borno state, a semi-desert region that once hosted one of West Africa's oldest medieval Islamic empires.
They are thought to be using poorly monitored borders with Cameroon, Chad and Niger to smuggle in arms and mount attacks.
Security sources say their strategy appears to be similar to that of the al-Qaeda-linked militants who overran Mali late last year, before the French forced them out in January: take over remote desert areas and establish a de facto rule there, then use that as a base from which to expand.
Growing links with jihadists across the Sahara region, and the fallout from Libya's war, are giving Boko Haram better access to weapons, funding and training.
Dozens of Boko Haram fighters attacked the Borno town of Bama last week, freeing more than 100 men from prison and leaving 55 people dead, mostly police.