Nigerian security forces staged lethal raids Saturday on suspected Boko Haram insurgents in the northern city of Kano allegedly plotting "suicide attacks" there and in the capital Abuja, the military said.

Five suspected "terrorists" and two soldiers died in gunbattles during the swoop on two addresses in Kano conducted by elite troops and domestic intelligence officers, military spokesman Captain Iweha Ikedichi said in a statement.

"Intelligence available indicates that the terrorists were in the process of finalizing plans to carry out simultaneous suicide attacks in Abuja and Kano respectively," he said.

Troops recovered a cache of arms and ammunition, he said.

Nigerian forces are waging an offensive against Boko Haram after President Goodluck Jonathan extended a state of emergency in three states in the volatile northeast in a bid to quell the Islamist group's bloody insurgency.

Kano is the stronghold of Boko Haram, a radical Islamist group that since mid-2009 has attacked Christians, Muslims, students, politicians and other groups opposed to its ambition to impose Sharia, or strict Islamic law.

Nigeria is Africa's most populous country and top oil producer. The northern half is mostly Muslim and the more prosperous south is predominately Christian.