Six other persons, who tried to help retrieve the duo, were also taken ill and admitted in a hospital for treatment, the police said.
Nasir Ahmad Lone (35) and his cousin Mohammad Hanief fell unconscious while digging a well at village Badran, 35 kms from here, last evening, the police said.
They said six persons were taken ill while retrieving the duo from the well.
All of them were rushed to hospital where the cousin brothers were declared brought dead, the police said adding they had apparently died of poisonous carbon monoxide gas emanating from a motor inside the well.