Vietnamese agriculture authorities say the current outbreak of bird flu has spread to two more provinces, bringing the number of cities and provinces affected by the disease to 10.
The national animal health department says about 2,000 birds were killed at a farm in Hoa Lu district in Ninh Binh province after 250 poultry died of the H5N1 bird flu virus there.
The department also says about 950 poultry have been killed at a farm in the northern province of Bac Ninh after bird flu was discovered there.
Vietnam had been praised by international public health authorities for its success in controlling the disease.
Last week, however, Vietnamese authorities said a farmer in Vinh Phuc province had tested positive for bird flu. He is Vietnam's first human case of the virus since late 2005.
The World Health Organization says bird flu has infected 93 people in Vietnam and killed 42 of them since 2003.
Some information for this report was provided by AP and Reuters.