Two more people were tested positive for the virulent H5N1 strain of bird flu in Turkey, the government said on Thursday.

The new test results brought to 18 the number of people who have contracted the disease in the country, where three people have died from the avian influenza.

Turkey has witnessed a renewed outbreak of bird flu across the country, after a first outbreak of the disease in October in the east was put under control.

At least 11 cities across the country have detected bird flu and over a dozen others may have been affected, according to the agriculture and rural affairs ministry.

At least 11 of Turkey's 81 provinces have reported outbreaks of bird flu, and Istanbul, the largest city in Turkey with a population of some 12 million, is the westernmost point where the virus has been found since it resurfaced in Turkey last month.

Experts fear that the highly contagious virus could mutate into a human strain that could cause a worldwide pandemic among human beings.

The H5N1 strain has so far killed over 70 people since it was first reported in Asia in 2003.