Tests have confirmed the lethal H5N1 strain of bird flu in chicken in Afghanistan, officials say.
Chicken is still available is some markets in Afghanistan
The virus has been confirmed in six samples taken from birds in Kabul and Jalalabad, a joint statement released by the UN and the government said.
These are the first cases of bird flu in Afghanistan.
Separately, in India's western state of Maharashtra 31,000 chickens have now been slaughtered after four more cases of the deadly strain were identified.
Following the detection of bird flu, the Afghan government has put an immediate ban on poultry imports from neighbouring Pakistan.
Nine hundred chicken farms have been closed in Jalalabad and the government and the UN plan to begin culling birds in the affected areas.
The BBC's Bilal Sarwary in Kabul reports that chicken has started disappearing from markets in Jalalabad and Kunar but are available elsewhere in Mazar-e-Sharif and Herat.
UN and Afghan government officials say a public awareness campaign about the virus is going to be launched.
Six other samples from the southern Afghan province of Kandahar and Kunduz in the north tested negative, officials say.
"Thus far in Afghanistan, avian influenza remains confined to the bird population with no human cases reported," the statement released in Kabul said.
"It is imperative that the human population is protected."
India mass slaughter
In India, some 7,000 birds have been slaughtered since operations began on Wednesday night in the Jalgaon district of Maharashtra state, a senior official told the BBC.
Hundreds of thousands of birds were destroyed in Maharashtra after India's first bird flu outbreak last month.
The virus later spread to some poultry farms in neighbouring Gujarat state.
"Slaughtering of birds has begun in four villages from where the samples tested positive. We are also maintaining a surveillance of a 10km area around these villages," Jalgaon additional district magistrate Manik Gajaram Gursal told the BBC.
Farmers are to be paid 40 rupees (90 US cents) in compensation for each bird.
Mr Gursal said that the samples which tested positive were all from chickens in home poultries in the district.
Jalgaon has an estimated 1,35,000 birds in commercial poultries, and another 5,00,000 birds that people kept at home.
Mr Gursal said there was no reason to panic about a possible spread of the virus as there were only two poultries with 2,800 birds in the 10km (six mile) "surveillance zone" around the affected areas.
Medical teams have also arrived in the villages and their surrounding areas to carry out checks and treat anyone suspected to be infected with the bird flu virus.
There have still been no reported cases of the virus in humans in India - 95 samples collected from people with flu-like symptoms last month tested negative for bird flu.
The detection of bird flu in India last month led to sharp falls in the sale of poultry and poultry products.
India's parliament, military, railways and major airlines temporarily stopped serving chicken and eggs, despite government reassurances that they were safe to eat if cooked properly.
The virus does not at present pose a large-scale threat to humans, as it cannot pass easily from one person to another.
However since 2004 about 100 people have died of the H5N1 strain - most of then in South-East Asia.
Experts fear the virus could mutate to gain this ability, and in its new form trigger a flu pandemic, potentially putting millions of human lives at risk.