The World Health Organization, fearing a killer flu pandemic may be on the way, is stepping up efforts to ensure governments around the globe are ready to fight it, a top official said on Wednesday.

The alarm has been sounded by the H5N1 strain of bird flu, which has become endemic in a number of Asian countries and which health officials fear could eventually mutate into a lethal new virus that will spread rapidly among humans.

The United Nations health agency, which sees a potential death toll of two million to seven million as a “best case scenario” for an outbreak, wants to tighten international cooperation and speed governmental battle plans.

“We have been stepping up our level of preparedness in the last month. Our level of concern is increasing,” Dr Klaus Stohr, head of the WHO’s global influenza program, told Reuters.

The worst hit countries so far have been Thailand, where the virus has killed at least 12 people, and Vietnam, where 20 have died.

“It would not be unexpected that the number of avian flu cases will increase with the onset of winter and we have to get our act together,” Stohr said.

International health officials have warned for years that a flu pandemic is overdue, because the last one, which killed between one million and four million, occurred back in 1968.

Even that toll pales against the 20 to 50 million thought to have died during the so-called “Spanish” flu outbreak of 1918.

“WHO and influenza experts worldwide are concerned that the recent appearance and widespread distribution of an avian influenza - Influenza A/H5N1 - has the potential to ignite the next pandemic,” the Geneva-based agency said in a statement on its Web Site.

It was impossible to predict just how deadly any such outbreak would be, because that would depend on various factors, including the virus’ virulence and the ease of transmission.

“The global spread of a pandemic cannot be stopped, but preparedness will reduce its impact,” the agency added.

As part of its campaign, WHO was overseeing the drafting of an international plan of action, laying down how governments and the WHO itself would react to any outbreak, Stohr said.

Health experts would put the finishing touches at a three-day meeting at WHO headquarters, starting next Monday.

“The concern is not just about the dying, it is the hundreds of millions that will be sick and who are going to flood into hospitals,” Stohr said.

Other measures included a network of hospitals and clinics in the five or six Asian nations seen as most vulnerable to the virus - Vietnam, Thailand, Indonesia, Malaysia, Laos and Cambodia.

The network, which should be up and running by next February, would standardize sampling of viruses as well as other techniques so that a critical mass of information on any outbreak could be quickly built up, Stohr said.

The WHO was also putting together a “checklist” which countries could use to assess their state of readiness.

“It is of central importance that…states…develop their own preparedness plans…some plans are far from complete and many…have yet to begin,” WHO warned in its statement.