The Ethiopian government is forcibly displacing tens of thousands from their land to make way for state-run sugar plantations, a campaign group has said.
The displacements are happening in the country's Omo Valley, according to a report by the New York-based Human Rights Watch (HRW).
The valley, a World Heritage site, is also the site of a controversial dam.
The Ethiopian government has denied forcing anyone from their homes and says the project will create jobs.
HRW says that in order to make space for the plantations, government security forces are compelling communities to relocate from their traditional lands, using violence and intimidation.
In its report, the campaign group says that at the time of its visit to the area - in June 2011 - "military units regularly visited villages to intimidate residents and suppress dissent related to the sugar plantation development". It added that "soldiers regularly stole or killed cattle".
These allegations were denied by government spokesman Bereket Simon.
"There is no forcing out of people from their residence, if there is any reason to relocate people, then it is based on... open communication," he told the AFP news agency.
The sugar plantations will be irrigated in part by the Gibe III hydropower project, the group says.
The dam, which would become Africa's largest and the fourth-biggest in the world, has provoked much controversy.
Flooding effect of dam on Omo River
The Ethiopian government says that the project must be completed in order to bring energy and development to the country.
But campaigners fear it will fuel conflict over already scarce water resources, and rob communities of their livelihoods.
According to the report, previously unpublished Ethiopian government maps show plans for sugar plantations covering nearly a quarter of a million hectares.
The maps, HRW says, also show processing factories, irrigation channels and large tracts of land reserved for other forms of commercial agriculture.
The group says that if the plans go ahead they could affect at least 200,000 people in the Omo Valley and another 300,000 Kenyans living across the border around Lake Turkana, which derives up to 90% of its water from the Omo River.
The Ethiopian government has said that the dam's impact on Lake Turkana will be negligible.
HRW describes the region as among the most ecologically and culturally diverse areas on the planet and says it is currently home to eight different agro-pastoral communities.
"Ethiopia's ambitious plans for the Omo Valley appear to ignore the rights of the people who live there," said Ben Rawlence, of Human Rights Watch.
"There is no shortcut to development; the people who have long relied on that land for their livelihood need to have their property rights respected, including on consultation and compensation."
Many other African countries are reserving huge tracts of land for commercial agriculture - often leased by foreigners in order to export the crops cultivated there abroad.