Yola - Nigerian forces are attacking Islamist strongholds in the northeast and an offensive is under way to wrest back territory from Boko Haram insurgents.
Soldiers raided areas in the Sambisa Game Reserve, a remote savannah of some 500 sq km (200 sq miles) in Borno state where Islamists have established bases, said two sources who spoke on condition of anonymity. They gave no further details.
Preparing for possible further action across three frontier states where President Goodluck Jonathan declared a state of emergency on Tuesday, the armed forces also deployed jet fighters and helicopter gunships to the region.
Rights groups said they feared for the safety of civilians from combatants on both sides, but Jonathan's move enjoys widespread public support after more than three years of trying to contain the insurgency without notable success.
It follows an upsurge in violence against government and Christian targets in the northeast by Islamists who want an Islamic state in Nigeria.
Africa's most populous nation's 170 million people are split evenly between Christians, who dominate in the south, and Muslims, who are the majority in the north.
Little detail was available from Sambisa. Nigerian forces have attacked Islamist bases in the area of the game reserve before, as recently as February, to rout militants seen as the biggest security threat to Africa's top energy producer.
The emergency affects the semi-desert states of Borno, Yobe and Adamawa, which variously border Niger, Chad and Cameroon and cover some 150,000 sq km (60,000 sq miles) - an area similar to England or Illinois, but with a population of only 10 million.