Nigerian veterinary teams were killing thousands of birds in two northern Nigerian states on Friday to halt the spread of fresh cases of the deadly H5N1 virus.

Nigeria was the first West African country to register bird flu when the disease jumped from Asia to Africa last year. Government veterinary teams slaughtered more than 900,000 birds in 2005, according to Nigeria's Agriculture Ministry. But sporadic outbreaks continued, with the last case reported in September in a suburb of Nigeria’s largest city Lagos.

Junaid Maina, Nigeria's national director of livestock, said new cases of the virus were confirmed this week in northwestern Sokoto and nearby in Katsina state, 800 kilometres northeast of Abuja. “Our teams are out there now culling birds,” Maina said.

Sokoto's cases are the first ever in the state, while Katsina is among 14 of Nigeria's 36 states struck last year. More than 18,000 birds have been culled in the two states since the beginning of the week, with more than 15,000 killed in Sokoto alone, an official involved in the operation told IRIN.

Most of the infections were in commercial poultry farms as supposed to family smallholdings, and compensation is being paid immediately to the farmers, the official said. “Any farm with any sign that looks like avian influenza, we simply depopulate and pay compensation,” the official said.

Funding has been provided under a scheme supported by the World Bank for immediate compensation of farmers whose birds have been killed by the veterinary teams.

Scientists fear the deadly H5N1 strain, which mainly affects birds but has been responsible for over 100 human deaths, could mutate into a strain transmittable between humans and spark a global pandemic.

More than 600 Nigerian animal health officials have been trained under a scheme funded by the European Union and the Food and Agriculture Organisation to undertake a nationwide surveillance to track bird flu. The experts will be deployed nationwide later in January, agriculture officials said.