A police station in Assam's Nagaon district was set afire by a mob on Saturday following an alleged case of custodial death of a local resident, a top police official said.

Three of those involved in the arson were arrested and operations are on to nab the others, the official said.

The mob had set ablaze the Batadrava Police Station and several two-wheelers in the afternoon following the death of a fish trader who was allegedly detained by the police late on Friday evening when he was going to take a bus for Sivsagar.

It was not clear why he was detained.

Nagaon Superintendent of Police Leena Doley said, Some miscreants had attacked the Batadrava Police Station in the afternoon and set it ablaze."

The family members of the fish trader of Salonabori village claimed that the police had demanded Rs 10,000 and a duck as a bribe for his release, and his wife visited the police station with a duck in the morning. When she returned with the money later, she learnt that her husband had been taken to Nagaon Civil Hospital. After reaching there, she found him dead, they claimed.

Alleging that the man died because of torture, villagers gheraoed the police station, allegedly assaulted on-duty police personnel and then torched the police station.

Videos of the incident showed a woman sprinkling some inflammable liquid on two-wheelers parked in front of the police station and setting them on fire.

The blaze engulfed the police station soon after and fire tenders later brought the flames under control. The SP, who visited the spot after the incident, said the police are analysing all video footage available.

On the allegations that the police demanded a bribe to release the man, Doley said all the charges will be investigated and if anyone is found guilty, steps will be taken.