GENEVA – The World Health Organization (WHO) voiced concern on Friday at a confirmed outbreak of swine flu in the United States and what it called more than 800 human influenza-like cases in Mexico, including about 60 deaths.

The United Nations agency said it had activated its Strategic Health Operations Center (SHOC) -- its command and control center for acute public health events -- but could not say whether it was considering issuing a travel advisory.

U.S. public health officials said on Thursday that seven people had been diagnosed with a new kind of swine flu in California and Texas, while Mexican authorities were due to announce test results later on Friday, WHO spokesman Gregory Hartl said in Geneva.

We are in daily contact with U.S., Canadian and Mexican authorities, Hartl told Reuters.

The U.S. Centers for Disease Control and Prevention said that the virus was a never-before-seen mixture of viruses typical among pigs, birds and humans. All 7 American patients had recovered.

WHO spokeswoman Fadela Chaib said Mexican authorities had noticed unusual activity at the end of the flu season in March and April.

To date there have been some 800 suspected cases with flu-like illness, with 57 deaths in the Mexico City area.

Similar cases have since been found in San Luis Potosi in central Mexico. The number of suspected cases is 24 suspected cases and 3 deaths, she told a news briefing.

Mexican Health Minister Jose Angel Cordoba said that it was cancelling classes for millions of children in the heart of the country on Friday after influenza killed around 20 people in recent weeks. Mexico's flu season had extended for longer this year.