By Elizabeth Blunt
BBC News, Addis Ababa
The detainees are said to be allied to self-exiled politician Berhanu Nega
Ethiopia's authorities say they have arrested 35 people who were allegedly plotting to overthrow the government.
All are said to be members of Ginbot 7 (15 May), an opposition group based outside Ethiopia and led by the self-exiled politician Berhanu Nega.
The Ethiopian government say the people arrested in Friday's raids fall into two groups: some were soldiers and others civil servants.
A government spokesman said they would be charged in court early next week.
Ermias Legesse said the group was an illegal organisation because it had not been registered as a political party and because its leadership had made statements in the US, indicating that it wanted to overthrow the government by unconstitutional means.
Mr Ermias said that during raids on the homes of the suspects, weapons had been found, including land mines, as well as military uniforms and copies of the group's future plans.
Berhanu Nega was one of the most charismatic opposition figures at the time of the last elections in Ethiopia in 2005 and if all had gone well he would have become mayor of Addis Ababa.
But he was arrested along with other prominent opposition figures and tried for treason, sentenced to life imprisonment, then pardoned and released.
Along with several of his colleagues he travelled abroad after his release, but while most of the others have returned to Ethiopia and are now organising themselves as a legitimate opposition party to fight next year's elections, Dr Berhanu chose to stay in the US, saying that the situation in Ethiopia was such that the government could not be changed by constitutional means.