The UN-agency said countries should implement infection control measures and procedures to reduce human exposure to birds and mammals potentially infected with bird flu or other animal influenza viruses.
The WHO said it strongly advises that people consume only pasteurized milk, in which bacteria and viruses have been killed, and avoid consuming raw milk.
"The virus has been detected in milk and its potential role in transmission is being investigated," the agency added.
One in five commercial milk samples tested in a nationwide survey contained particles of the H5N1 virus, the US Food and Drug Administration said late on Thursday, suggesting the outbreak is more widespread in the country than previously thought.
US officials have strengthened measures to contain the first known outbreak of the H5N1 virus in dairy cows, which has now spread to 33 herds in eight states.
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