More than 50,000 people in the Ethiopian capital, Addis Ababa, have demonstrated against government plans to renew border talks with Eritrea.
Demonstrators say the proposed deal is a sell-out
Opposition leaders told the rally that a new peace plan with Eritrea would not right the wrongs of the peace treaty that ended a bitter border war in 2000.
They say the deal threatens Ethiopia's territorial integrity.
Prime Minister Meles Zenawi agreed in principle in November to accept a border ruling it had disputed.
The peace plan "aims at giving away part of Ethiopia's land, which was won through the blood and sacrifices of tens of thousands of its gallant sons", opposition activist Gebru Asrat told the crowd, according to Reuters news agency.
It "did not serve the interest of Ethiopia and its people - it was a sell out", he said to cheers from supporters.
The disputed village of Badme was attributed to Eritrea in a 2002 ruling by an independent boundary commission, set up under a peace treaty that both countries signed in Algiers in 2000.
Ethiopia initially rejected the decision, saying it could cause further conflict. It accepted the ruling in November 2004 but Mr Meles did not mention Badme by name.
Correspondents say the rally was designed to prevent Mr Meles gaining support for his initiative ahead of Ethiopia's general election in May.
Tens of thousands of people were killed when Eritrea and Ethiopia fought a two-year border war which began in 1998.
The conflict started after Eritrean troops invaded Badme, which was under Ethiopian administration.