Talking to journalists after inspecting the party office on Wednesday, Koirala termed the blast ´cowardice´ and said that it was carried out by the forces that were against the republic and new constitution drafting process.
Koirala said such an act would not distract the party from constitution drafting and state restructuring processes.
Senior leaders including the party´s vice president and parliamentary party leader Ram Chandra Poudel, Gopal Man Shrestha, Ram Sharan Mahat and Romi Gauchan Thakali also inspected the office.
Poudel asked the government to book the guilty at the earliest. Nepal Defense Army carried out the blast, causing minor damages to the office.
Meanwhile, issuing a press statement Rastriya Janashakti Party denounced the blast and urged the government to immediately book the guilty. The party also expressed concern about the deteriorating law and order situation.
Similarly, the CPN-UML also condemned the bomb explosion at the NC office. Issuing a press release on Wednesday, the party said the regressive elements trying to hinder the constitution writing process were behind the blast, RSS reported. The party also demanded arrest of the perpetrators.
The Home Ministry also condemned the blast and said a few persons have been arrested on suspicion of involvement in the blast. It said security bodies have been directed to book the culprits and appealed to all to help the police in investigation.
Prime Minister Madhav Kumar Nepal also vowed to book the perpetrators involved in the incident.
Train with 53 bogies carrying blast arrives in Janakpur