Four persons were killed and three others injured while they were allegedly making bombs in a village near Bangladesh border in the district early on Monday, ahead of the last phase of polling on May 5 in West Bengal.
An explosion occurred when bombs were being made in the house of one Giasu Sheikh in Jaunpur village under Baishnab Nagar Police Station at about 1 am, Superintendent of Police Syed Waqar Raza said.
Incidents of post-poll violence have been reported from various parts of the state.
One person died on the spot and three others succumbed to their injuries in Malda Medical College and Hospital.
The deceased were identified as Kalam Sheikh (35), Simu Sheikh (28), Surup Sheikh (35) and Alam Sheikh (30).
Three persons were admitted in hospital, said the SP who himself visited the spot in the morning.
He said local rowdies were involved in the incident, adding, Giasu has been absconding.
Polling was held in the district on April 17 in the second phase of the West Bengal Assembly polls.