Human Rights Watch urged Nepali authorities Friday to "immediately investigate and bring to justice" the people responsible for "killings and other violations" during protests about a new constitution.
The group said at least 45 people were killed during the protests this year in August and September.
Nepal decided to deliver a new constitution following the country's devastating earthquake in April.
HRW said, "After nearly a decade of political stalemate," the country chose that vulnerable time to go forth with plans for a new constitution, leaving little time for consultations.
Charter sparks protests
The new charter was published in September, sparking protests in ethnic minority areas, primarily in the far west and the southern plains of the country. Protesters were demanding greater political autonomy based on prior agreements.
HRW said in a 44-page report entitled "Like We Are Not Nepali: Protest and Police Crackdown in the Terai Region of Nepal" that 25 people were killed in that region alone, including 16 members of the public and nine police officers.
The human rights group said in a statement it did not find any evidence "that any of these victims were posing a threat at the time that they were killed."
"While the drafting of a rights-respecting constitution is an emotional issue in Nepal, disagreements cannot be resolved by committing serious human rights abuses," said Brad Adams, the Asia director of HRW. "The government has the responsibility to ensure there are impartial and effective investigations and cannot simply look the other way."
HRW said it found "credible reports of serious human rights violations" by security forces sent out to contain protests in the Terai region.
HRW said its researchers unearthed eyewitness accounts of police activity that included "breaking into homes to beat occupants, including women and elderly; using racial insults during violent incidents or threatening to kill members of the public; arbitrarily beating passersby; and harassing villagers belonging to communities opposing the new constitution."
The human rights group said its investigation also found eight of the nine police officers were killed on August 24 in Tikapur when some protesters encircled and attacked a small group of outnumbered police.
"Nepal's new leadership should take immediate steps to stem the tide of abuse that has overtaken Nepal the last few months," Adams said. "The government needs to order investigations, and publicly call on all security forces to desist from any excessive use of force."
Khadga Prasad Sharma Oli replaced Sushil Koirala as prime minister earlier this week.