The United Nations is warning that bird flu outbreaks have spread to 15 countries, making the disease a global threat that requires close monitoring.

The Food and Agriculture Organization of the United Nations released a statement Thursday, calling for more monitoring and greater efforts to contain the virus.

The outbreaks have been reported since December and involve mostly domesticated poultry infected with the virulent H5N1 strain.

The FAO's chief veterinarian, Joseph Domenech, says while there has been global progress in containing the bird flu, the crisis is far from over.

He says the outbreaks are especially worrisome in Indonesia, Bangladesh and Egypt, where the virus has spread despite major efforts to control it.

The other nations where bird flu outbreaks have been reported since last month are Benin, Burma, China, Germany, India, Iran, Israel, Poland, Russia, Ukraine, Turkey and Vietnam.

Some information for this report was provided by Bloomberg.