At least three cadres of United Democratic Madhesi Front (UDMF) died in the clash in Rajbiraj of Saptari as clash erupted when UDMF Cadres tried to block the UML's program on Monday.
The security forces had to use force in order to bring the condition under control.
Sanjan Mehata, Aananda Sah and Pitamber Mandal were identified as deceased.
The clash also resulted in injuries of eight people who are undergoing treatment in Sagarmatha Zonal Hospital.
The Madhesh based parties have withdrawn its support for the Pushpa Kamal Dahal-led government with the clashes in the Saptari district.
They have also called for two day strike in the Terai region and will continued there protest.
Following the clashes, the Chief District Officer (CDO) of Rajbiraj announced a curfew in the region.
The government has called the CDO of Saptari to center after the event on Monday.