Considering the rapidly increasing number of confirmed swine flu cases, WHO officials have decided to consider raising the pandemic alert level to phase 5.

Swine Influenza (swine flu) caused by type A influenza, regularly leads to influenza outbreaks among pigs. The virus does not normally infect humans.

Confirmed sufferers in the United States and Mexico, however, are believed to have spread the disease to their families and others in close contact.

The alert level was increased to 4 on Monday, and WHO officials now say they will be forced to declare a phase 5 alert soon.

"We're still awaiting for a final confirmation from the US authorities, but it appears that there's a number of cases in New York which appear to be human-to-human transmission," WHO spokesman Gregory Hartl told a news briefing.

The United Nations agency also raised its alert level to 4 on Monday as the virus was detected in several European countries.

Mexican authorities say the new strain has killed up to 149 people in Mexico. About 64 confirmed cases have been reported in five US states.

PKH/HGH