Agriculture Minister Akinwumi Adesina said the first cases were confirmed on a commercial farm in the northern city of Kano and at a live bird market in Lagos State on January 8.

"While we quickly confirmed that the cases were due to H5, we could not at the time determine the biotype. We have now confirmed that the cases were due to the H5N1 virus," he added.

"We are taking all measures necessary to ensure that public safety is protected and that the poultry industry is not significantly affected by the spread of the bird flu."

Adesina told reporters in Abuja that the five states involved were Lagos and Ogun in the southwest, Delta and Rivers in the south and Kano in the north.

Fifteen commercial farms and nine live bird markets were affected.

"As at today January 21, 2015, a total of 139,505 birds have been associated with bird flu exposures, with 22,173 (15 percent) mortality recorded," he said.

Kano was the worst affected, with 103,445 bird reported as exposed to infection. Of those nearly 16,000 had died, he added.

The H5N1 strain of the bird flu virus has killed more than 400 people worldwide since it first appeared in 2003, most of them in southeast Asia.

But Adesina said there was "no cause for alarm" and "we are not in a state of any epidemic". The risk to humans was small, he said, but urged enhanced hygiene procedures to be taken.

"I can assure you that Nigeria is managing the recent outbreak with strong determination, purposefulness and aggressiveness," he added.

Biosecurity measures introduced included comprehensive surveillance of poultry farms across the country, quarantine and decontamination of outbreak sites, he said.

Nigeria H5N1 bird flu now in 7 states, suspected in 140,000 birds: minister