Bird flu [Images] has spread to fresh areas in the affected West Bengal districts of Howrah, Birbhum and Nadia, while a large number of chickens died in North 24 Parganas, which is still not among the 13 affected districts.

In Howrah, poultry samples from Uttar Panchla village were tested positive at laboratory and fresh culling operation initiated within the five-km radius of the area, District Magistrate Khalil Ahmed said.

The administration had so far culled 1.5 lakh chicks in the district where bird flu had earlier been reported in two blocks -- Sankrail and another village of Panchla block -- in the past three days, he said.

In Birbhum, samples from Alunda village in Suri block-1 of Birbhum tested positive and in Nadia district, where culling has been completed, it spread to Kalyani, official sources in the districts said.

Animal Resources Development Minister Anisur Rahaman said over 4,000 chicken died at Baduria in North 24 Parganas district, adjacent to Kolkata, with samples being sent to Bhopal. He said culling had been ordered in a five km radius of the fresh affected areas.

In Nadia district, it spread to Kalyani with reports from Harijan pally Ward number 2. Culling would begin from Wednesday, he said.

A total of 25 lakh chicken had been culled all over state, Rahaman said.

"The target may be little higher considering the fresh outbreak, but we have asked the districts to complete culling by Wednesday," Rahaman said.

The state government also sought information from Bangladesh on the strains of the avian influenza to source the origin of the viral infection.