GENEVA (Reuters) - Mexico has reported a third possible outbreak of swine flu in Mexicali, near the U.S. border, with four suspect cases and no deaths to date, the World Health Organisation (WHO) said on Friday.

The WHO also said that the viruses in the outbreaks in Mexico and the United States had not been detected in pigs or humans before but were proving sensitive to Tamiflu. Known generically as oseltamivir, the pill by Swiss drugmaker Roche Holding can both treat flu and prevent infection.

"Because there are human cases associated with an animal influenza virus, and because of the geographical spread of multiple community outbreaks, plus the somewhat unusual age groups affected, these events are of high concern," the Geneva-based agency said in a statement.

(For the WHO statement go to: here )

(Reporting by Stephanie Nebehay; Editing by Jonathan Lynn)