Ethiopian security forces have killed at least 140 people taking part in mass anti-government demonstrations since November, activists say, according to US-based Human Rights Watch (HRW).
The protests have been sparked by fears that a plan to expand the capital’s administrative control into the Oromia region will displace Oromo farmers.
HRW also called for the release of an Oromo politician arrested last month.
The government has accused Oromo protesters of links with terror groups.
Last month, officials said five people and an undisclosed number of security personnel had died in the protests.