Two brothers and their cousin were killed, and at least seven others were injured in a clash between rival groups over control of illegal sand trade in Madaripur's Sadar upazila on Saturday.
The deceased were identified as Saiful Sardar, 50; his brother Atabur Sardar, 40; and their cousin Palash Sardar, 17. All three were from Khoajpur village in the upazila, said Chhatak Chakma, additional superintendent of Madaripur Police (Sadar Circle).
According to locals, there had been a long-standing dispute over illegal sand extraction in the Arial Khan River between Md Shahjahan Khan and Saiful at Khoajpur union in the upazila.
Tensions erupted into a deadly clash between their supporters around 12 pm on Saturday.
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At one point, the victims were attacked with sharp weapons, leaving Saiful and Atabur dead on the spot.
Among the injured, three were transferred to Dhaka Medical College Hospital for advanced treatment, where Palash Sardar succumbed to his injuries while undergoing treatment.
Additional police and army personnel have been deployed to control the situation, said the additional SP.
Two individuals have been detained for questioning, he added.