The blast occurred near Pashupati Plastic Industry at 9.30 p.m. Manager of the industry, Bijay Prasad Chaurasia, when the assailants threw the bomb at him when he was riding motorcycle on his way home.
Injured Chaurasia is being treated at Narayani Sub-regional Hospital. He is out of danger.
Some three months ago, a criminal gang from India allegedly asked him to pay them Rs 300,000.
Meanwhile, a little-known armed group, Tarai Army, has owned up the attack on Chaurasia.
Birgunj has experienced a spate of bomb blasts recently. Police say armed groups in the Tarai usually detonate improvised explosive device (IED) once they are refused extortion.
Related story
Stars, KIEC Birgunj win in Birgunj Premier League
