Vietnam (search) on Monday reported two new suspected cases of bird flu (search) in humans as outbreaks among poultry spread to all parts of the country, officials and state-controlled media said.

Tests were being conducted to determine whether the two patients being treated at Hanoi's Hospital of Tropical Medicine for Tropical Diseases (search) contracted bird flu, said hospital director Nguyen Duc Hien.

Tests on a 48-year-old man from the northern province of Thai Binh who died Saturday were negative for bird flu, Hien said. The man was initially suspected of having contracted the disease.

The People's Army newspaper identified the two suspected cases as the younger brother of the 48-year-old man and a 62-year-old man from Hanoi.

Bird flu outbreaks among poultry have been reported in central Quang Nam and Ninh Thuan provinces, the latest region to have been hit by the disease, the Department of Animal Health said on its Web site Monday.

Earlier, 16 provinces, mostly in southern Vietnam, had reported outbreaks since the beginning of this year, killing or forcing the cull of more than 230,000 birds.

Animal health experts have warned that cooler temperatures and the increase in movement of poultry ahead of the Lunar New Year festival in early February favor the spread of the virus.

Over the past three weeks, Vietnam has reported four human deaths from bird flu — the country's first string of deaths since early September.

Two other people who tested positive for the H5N1 strain of the bird flu remain in critical condition.

Bird flu has killed 24 people in Vietnam and 12 in Thailand over the past year.