Dozens of people have been killed in a military strike launched by Nigerian army since Thursday night in the northern part of the West African country, according to security sources.

The casualties include three soldiers involved in the army's unprecedented action against insurgents of the Boko Haram sect, which suffered the heaviest losses since emerging in 2009, the sources disclosed on Friday.

Earlier in the day, the military said a number of suspected gunmen believed to be the Boko Haram sect were killed in Daura in Katisna State, the home town of opposition leader Muhammadu Buhari.

The military spokesman, Maj.-Gen. Garba Wahab, told reporters in the city of Kaduna that the army and security personnel had cordoned off three areas in the city and were conducting a house- to-house search to fish out some of the wounded gunmen who were believed to force their way into homes of local residents.

The army is also coordinating with security agencies in neighboring Niger in the action, 80-90 percent of the gunmen are not Nigerians, according to the spokesman.

Wahab said the gunmen had attacked four banks and stolen some money, adding that a vehicle loaded with the stolen cash was recovered, in addition to four AK-47 rifles.

He said the operation to fish out the culprits was still on, advising residents of Daura and the local government areas of Baure, Sandamu, Mashi, and Dutsi to cooperate with security agents by reporting suspicious movements around them.

Wahab appealed to journalists to support security agencies in the fight against terror, saying it was the collective responsibility of all well-meaning Nigerians to work for the peace and stability of the nation.

The military took action barely 48 hours after President Goodluck Jonathan declared a state of emergency in the northern states of Borno, Yobe and Adamawa.

Last month, president Jonathan tried but failed to reach a ceasefire with Boko Haram, which, based in the northeast of Nigeria, declares war against Western education and seeks to enshrine the Islamic sharia law in the Constitution.

It has claimed responsibility for a series of attacks in northern Nigeria, causing thousands of casualties in the past years, including women and children.