Leading a multinational team of medical experts to mobilize Southeast Asian nations against bird flu, Health and Human Services Secretary Michael Leavitt (search) said Monday the likelihood of a flu pandemic in the future is "very high."

Leavitt, accompanied by the director of the World Health Organization (search) and other top health professionals, is visiting Thailand, Laos, Cambodia and Vietnam to seek their collaboration in preparing for the anticipated public health emergency.

In the past 2 1/2 years, the H5N1 (search) strain of bird flu has swept through poultry populations in Southeast Asia, also infecting humans and killing at least 65 people. The virus does not pass from person to person easily, but experts believe this could change if the virus mutates.

Leavitt said there were three influenza pandemics in the last century and "the likelihood of another is very high, some say even certain."

"Whether or not H5N1 is the virus that will ultimately trigger such a pandemic is unknown to us," he said at a news conference. "The probability is uncertain. But the warning signs are troubling. Hence we are responding in a robust way."

Leavitt said his delegation reviewed Thailand's plan of action against bird flu and that a draft of a comprehensive U.S. plan would be released in a few days.

He described "containment" as the first line of defense against bird flu, and encouraged strengthening public health systems to find out as early as possible of any cases of human-to-human transmission.

Another strategy was the production and use of antiviral drugs and vaccines. Leavitt said that scientists have developed a vaccine based on bird flu samples from Vietnam, but the effective dosages are six to 12 times that used for combating the so-called seasonal influenza that has become common around the world.

Also Monday, Turkey and Romania slaughtered thousands of domestic fowl after both countries said they found the disease in birds, and the European Union and other countries banned the import of poultry from the two nations.

However, bird flu has not been confirmed by expert laboratories and it is unknown whether the poultry deaths in either location involve the H5N1 strain.

In western Turkey, military police quarantined the area around two villages — Kaziksa and Salur — in Balikesir province, as veterinarians killed thousands of poultry. Other fowl, including pigeons, and stray dogs also were to be killed as a precaution, said Nihat Pakdil, deputy undersecretary of the Agriculture Ministry.

Preliminary tests detected bird flu at a farm in Turkey after some 1,800 birds died last week. Scientists have narrowed the disease in Turkey down to an H5 type virus but have not determined whether it is the H5N1 strain that health officials are worried about, Agriculture Ministry official Beytullah Okay said.

Samples from the dead birds were sent to a special EU laboratory that was expected to determine by Wednesday whether the animals where infected with the strain. Britain's agricultural agency said it also asked Turkey to send samples to its lab and hopes to have results within two days.

A team of EU veterinary experts was on its way to Turkey to assess the situation, according to a spokesman at Britain's Department for Environment, Food and Rural Affairs, which runs the expert lab.

In Turkey, 2,500 turkeys and 400 chickens have been destroyed so far, Okay said. Two farm owners and five other people were treated as a precaution. Authorities also banned hunting in the region and a poultry market in Bursa was closed down.

In eastern Romania, some 40,000 birds were to be slaughtered in coming days, authorities said.

"I think it's better to take these preventive measures now," even without confirmation of H5N1, Romanian Prime Minister Calin Popescu Tariceanu said.

The EU decided to ban the imports of live birds and feathers from Turkey. Greece, Ukraine and the Kosovo region of Serbia-Montenegro banned poultry imports from both Turkey and Romania.