DSP Ramesh Kumar Khadka said lawmaker Jangilal Raya, Binay Karna, Anish Sathi and Bijay Raya were arrested as they attempted to set ablaze the police post after vandalizing it.
Police opened five rounds of bullet in air to detain protesters.
Security personnel from District Police Office, Sarlahi, nearby area police offices and Border Security Office have reached the incident to stop the situation from further worsening.
The indefinite shutdown enforced by Madheshi Front took violent turn on Friday after demonstrators torched the Haripurwa-based Temporary Police Post.
Police constable arrested for “attempt to rape”