Attacks attributed to Boko Haram have risen since the group took responsibility for the bombing of U.N. offices in Abuja last year.
Nigeria has been on a heightened state of alert since December when the group also claimed responsibility for Dec. 25 attacks targeting Christians.
A Nigerian military officer who spoke to the United Nations' humanitarian news agency IRIN on condition of anonymity said the group blended in easily with the local population.
"We are dealing with a guerrilla insurgency where the enemy is faceless and can blend with ordinary civilians," he said. "Boko Haram elements are hardly recognizable by appearance, they can only be known when they carry arms and strike and they then dissolve into the population which makes our operation very difficult."
Analysts specializing in African affairs have said Boko Haram is a domestic threat that requires careful consideration of non-military deterrence. The government, however, declared a state of emergency in parts of the country and put more troops on the streets.
IRIN estimates at least 100,000 people are internally displaced by the Boko Haram threat. The group aims to establish an Islamic state in a country divided largely along Christian and Muslim lines.