"An unidentified group detonated the IED targeting Tumlingtar-based office of Arun-3 Hydropower Project at around Saturday midnight," Chief District Officer Shiwaraj Joshi told The Himalayan Times.
Joshi further said that there were no casualties in the explosion, adding it caused minor damage to the office. An investigation has been launched to probe the attack.
Till now, no one has claimed responsibility for the explosion.
The project is scheduled to be completed by 2020.
Earlier on April 17, a minor explosion took place near a camp office of the Indian embassy in Kathmandu's Biratnagar area.
No injuries were reported and the office wall on the western side of the office was slightly damaged in the explosion. (ANI)