Two Cambodian girls have died from bird flu, health authorities said Tuesday, raising the toll from the deadly infection in the kingdom to four so far this year.

The victims, a 17-month-old girl and a nine-year-old girl, from the southern provinces of Kampot and Kampong Speu, died Monday in hospital, the World Health Organization said in a joint statement with the Cambodian health ministry.

Tests on the girls, whose villages had recorded recent deaths among poultry, confirmed they had contracted the H5N1 strain of avian influenza, the statement added.

Last week Cambodia said two people -- a 15-year-old girl and a 35-year-old man, had died from the H5N1 strain contracted while preparing infected chicken.

Cambodia has recorded 26 cases of H5N1 since 2003 with all but three of the victims dying.

The virus has killed 364 people worldwide since a major outbreak in 2003, according to WHO statistics.

It typically spreads from birds to humans through direct contact, but experts fear it could mutate into a form easily transmissible between humans, with the potential to trigger a pandemic.