Niger has become the third African country to have confirmed cases of the deadly strain of bird flu, experts say.
People can catch bird flu by handling infected poultry
Test results have confirmed several cases of the H5N1 virus, said the World Organisation for Animal Health (OIE).
Niger, one of the world's poorest countries, has a long border with Nigeria, where bird flu has killed thousands of chickens.
No human cases of the H5N1 strain have yet been found in Africa but the UN has warned of a possible regional disaster.
The H5N1 strain was found in domestic ducks near Nigeria's border, the OIE said.
"We've been officially informed that the presence of the virus has been notified on the sample from Niger but we are waiting for official documents to know... what type of strain it is," said Niger's government spokesman Mohamed Ben Omar.
OIE director Bernard Vallat said it came as no surprise that bird flu had spread from Nigeria to Niger.
"We know that the virus in Nigeria has invaded a large part of the country. The measures of confinement were not taken and transparency was not applied from the beginning, he said.
"Now we know that all of the neighbouring countries of Nigeria are under a very big threat."
Niger, like most West African countries, had banned poultry imports from Nigeria.
Earlier, Nigeria's Information Minister Frank Nweke announced that the H5N1 strain had been found in two more Nigerian states, taking the total to seven - mostly in the north and centre of the country.
One of the new states - Yobe - is on the border with Niger.
Bird flu has also been found in Egypt.
Last week, the UN's Food and Agriculture Organisation (FAO) recommended that Nigeria vaccinate poultry, saying the strategy of containment and slaughter of at-risk birds was not working.
There are also calls for clarification on the issue of compensation for farmers.
Almost 60% of poultry producers raise chickens in their backyards and health officials are worried that they would not tell the authorities if their birds fell ill.
Nigeria's Health Minister Eyitayo Lambo has admitted that planned compensation of 250 naira ($2) per chicken is inadequate as the market price is more than double that.
More than 90 people have died of H5N1 bird flu since the disease's resurgence in December 2003 - most of them in South-East Asia.
Experts say that cross-infection to humans is still relatively rare and usually occurs where people have been in close contact with infected birds.
But they say if the H5N1 strain mutates so it can be passed between humans, it could become a global pandemic, killing millions.