A video of the lynching went viral on social media
The two died while bathing in the Bajarghat area around 3am on Saturday, said Ruma Upazila UNO Md Shamsul Alam.
The dead were identified as United International University lecturer Shantanu Sarker, 25, and his friend Shahed Ehsan, 26.
The two had gone for a trip to Bogaikan Lake, the UNO said. The two returned to Ruma that afternoon and went to bathe in the Sangu River in Bajarghat and drowned.
The bodies of two tourists who drowned in the Sangu River were recovered, said Ruma Police Station OC Shariful Islam.