Nigeria said on Friday it had quarantined two poultry farms in the north and south of the country after detecting an H5 strain of bird flu in both, giving no further details on the strain.

Agriculture Minister Akinwumi Adesina statement said samples were taken from birds at the two farms, in the commercial hub Lagos and the main northern city of Kano, after they showed "unusual high mortality" rates.

The samples "tested positive for the H5 strain of avian influenza virus", the statement said, adding that samples had been sent to a laboratory in Italy for further testing.

A spokesman for the ministry was not able to elaborate on the virus strain's subtype.

Nigeria, Africa's most populous country and biggest economy, was the continent's first country to detect bird flu in 2006, when chicken farms were found to have the H5N1 strain. In 2007, it reported its first human death from the disease.

High pathogenic H5N1 bird flu first infected humans in 1997 in Hong Kong. It has since spread from Asia to Europe and Africa and has become entrenched in poultry in some countries, causing millions of poultry infections and several hundred human deaths.