The WHO is advising all member states to be vigilant for seasonally unusual flu or pneumonia-like symptoms among their populations - particularly among young healthy adults.
Officials said most of those killed so far in Mexico were young adults - rather than more vulnerable children and the elderly.
The committee has not recommended declaring an international public health emergency and raising the global pandemic alert level, a move that could lead to travel advisories, trade restrictions and border closures.
At least some of the cases show a new version of the H1N1 swine flu sub-strain - a respiratory disease which infects pigs but only sporadically infects humans.
The RC church has issued advice to its priests to help halt the spread of the flu
H1N1 is the same strain that causes seasonal flu outbreaks in humans, but the newly-detected version contains genetic material from versions which usually affect pigs and birds.
The virus is spread through coughs and sneezes and through direct and indirect contact between people.
Mexican officials have confirmed 20 deaths from the virus and are investigating dozens more.
Schools, museums and libraries have been closed across the capital's region and people are being urged to avoid shaking hands or sharing crockery.
Hundreds of public events have been suspended and schools in the Mexico City area have been closed until 6 May.
Two previously sold-out soccer matches were played in empty stadiums to avoid potentially spreading the virus.
Health officials are isolating individuals suspected of having the virus and inspecting their homes.
The Roman Catholic Church in Mexico has recommended measures to avoid further contagion at Mass this Sunday.
Priests have been told to place communion wafers in the hands of worshippers rather than in their mouths and to suggest to the congregation that kissing or shaking hands be avoided during the service.
In the US, 11 people are now known to have been infected with the new strain - seven people in California, two in Texas, and two in Kansas.
There are also eight suspected cases in New York City after 200 students at a high school fell ill.
Specimens were taken from nine students, and eight were determined to be probable cases of swine flu, said city health commissioner Dr Thomas Frieden.
Those samples are now being examined by the US Centers for Disease Control and Prevention (CDC).
No children had required hospital treatment and many had fully recovered, said Dr Frieden, but the school could remain closed out of "an abundance of caution".
He urged people to maintain basic hygiene, such and covering their mouths when coughing and sneezing, washing hands regularly and keeping surfaces clean.
Dr Frieden said most people would not need to take antiviral medication if they fell ill, unless they had an underlying medical condition.
CDC officials have said that with cases arising in so many communities, containment is unlikely to be feasible.
There is currently no vaccine for the new strain.
Swine flu is a respiratory disease found in pigs
Human cases usually occur in those who have contact with pigs
Human-to-human transmission is rare and such cases are closely monitored
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