Agriculture officials in the eastern U.S. state of Delaware are reporting a second poultry flock infected with what they say is a mild form of bird flu.
Authorities have identified the strain as the H7 virus, the same one found Sunday on another chicken farm about eight kilometers away.
State officials imposed an immediate ban on the sale of live poultry in the state, while insisting that the H7 virus is not a threat to humans.
Earlier Tuesday, China banned imports of all U.S. poultry. Japan, South Korea and several other Asian countries have also halted U.S. imports.
China is particularly sensitive to the growing threat of bird flu. Tuesday, the World Health Organization warned that China may be the next country to report human cases.
Nine countries plus Taiwan have reported bird flu. So far, human outbreaks have been limited to Thailand and Vietnam. Nineteen people have died in those two countries.
China has reported suspected or confirmed outbreaks of bird flu in nearly half of its 31 provinces. But it has not yet reported any human cases.