A member of Nepal's armed police was killed in the southern district of Mahottari on Friday after protesters dragged him out of an ambulance on its
way to a hospital and assaulted him, a police official said.
In a separate incident, police shot and killed three demonstrators in a neighboring district, bringing the death toll to at least 39 in protests that erupted in southern Nepal after a draft constitution was unveiled last month.
Nepal, which emerged from civil war in 2006, is in the final stages of preparing a long-awaited constitution that would carve the country of 28 million people into seven federal provinces.
Many in Nepal's southern plains, known as the Tarai, oppose the plan which would split their narrow region and merge the pieces into larger provinces with other ethnic groups.
Communities in the Tarai have traditionally close ties with India, and complain of widespread and entrenched marginalisation at the hands of political elites in Kathmandu.
"The area has been declared a riot-hit zone," said Kali Prasad Parajuly, chief district officer in Dhanusha, where the protesters were shot. "We are waiting to see if the army will be deployed."
Several Tarai towns are under curfew and the army has already been deployed to restore order in some areas.
On Friday morning, Nepal's three main political parties agreed to halt the constitution drafting process in an attempt to bring dissenting groups in the south on board.
But leaders of the Tarai Samyukta Madhesi Morcha, the chief agitating group in the region, have already rejected the government's invitation for dialogue, according to local reports, calling for the withdrawal of the army from the area, among other demands.