The UN High Commissioner for Human Rights has expressed concern over the "excessive use of force" by security forces in the troubled Terai region of Nepal, a statement said.
"Our human rights officers who have been monitoring events in Terai have observed violence by protestors, as well as incidents of excessive use of force by the armed police force and the Nepal police," Commissioner Louise Arbour said in the statement on Wednesday.
Since the outbreak of unrest almost three weeks ago 18 protesters and one police officer have been killed and hundreds injured during widespread rioting by Madhesi groups in the southern region.
"While I recognise the challenges police are facing — including attacks on themselves -- the security forces must employ force only in proportion to the actual threat faced," Arbour said.
Nepal's large Madhesi community that has long complained of discrimination and being shut out of power are seeking autonomy and increased political representation.
The violence has cast a cloud over the new government, which has pledged to hold elections this year to rewrite the constitution and decide the future of the monarchy.
"Ending discrimination and ensuring appropriate representation of excluded groups at all levels of decision making during this critical time will be essential to the success of Nepal's political transition," she said.
Arbour also called on the Nepalese authorities to guarantee the freedom and safety of all UN employees in the region.