US health authorities are attempting to develop a vaccine for the H7N9 bird flu virus that has so far killed five people in China.
With the number of confirmed infection cases climbing to 14, authorities in Shanghai have begun the mass slaughter of poultry at a market after the virus was detected there in samples of pigeon.
Noting an ongoing probe by Beijing, the Centers for Disease Control and Prevention, a US federal agency, said it was following the situation closely.
Its efforts will include "gathering more information to make a knowledgeable public health risk assessment, and developing a candidate vaccine virus."
The CDC is also "reviewing posted genetic sequencing of the H7N9 viruses and assessing possible implications in terms of the viruses' transmissibility and severity and whether existing influenza diagnostic tests need to be enhanced or new ones developed."
The World Health Organization this week played down fears over the strain, saying there was no evidence of human-to-human transmission, but that it was crucial to find out how the virus infects humans.
Like the H5N1 virus which typically spreads from birds to humans through direct contact, experts fear such viruses could mutate into a form easily transmissible between humans with the potential to trigger a pandemic.
The first two deaths from the virus, which had never before been seen in humans, occurred in February but were not reported by authorities until late March. Officials said the delay in announcing the results was because it took time to determine the cause of the illnesses.