By Barry Malone
ADDIS ABABA, May 6 (Reuters) - Relatives of a group accused of plotting to overthrow the Ethiopian government have been unfairly arrested by association in the Horn of Africa country, a rights group says.
Prime Minister Meles Zenawi's government said last month a group led by an Ethiopian-American professor had planned to use assassinations and bombings to provoke street protests and topple the government.
Addis Ababa says it arrested 40 former and current army personnel and members of a disbanded opposition group from a "terror network" it said was formed by Berhanu Nega, an opposition leader now teaching economics in the United States.
"Several may have been detained solely for their family ties to men who have expressed political opposition to the government," said Michelle Kagari of Amnesty International in a statement late on Tuesday.
"They should be released immediately."
The arrests represent the biggest roundup of opposition figures in Ethiopia since more than 100 opposition members were imprisoned after a disputed 2005 election.
They were released in a 2007 pardon deal but Birtukan Mideksa, the leader of the Unity for Democracy and Justice party, was rearrested last year after the government said she violated the terms of her pardon.
Amnesty say she is a "prisoner of conscience" and should be released.
The rights group also demanded those detained be named and said one -- the 80-year-old father of a London-based opposition leader -- was in urgent need of medical care.
Opposition parties routinely accuse the government of harassment and say their candidates were intimidated during local elections in April of last year.
The government denies that.
Ethiopia will hold national elections in June 2010 and opposition leaders have said the arrests are an attempt to jail potential candidates ahead of that poll.
The Ethiopian government's head of information, Bereket Simon, told Reuters that nobody would be arrested for being related to someone opposed to the government.
"Evidence is being prepared and will be considered by an independent judiciary," he said.
The accused are due to appear in court on May 11th. (Editing by Jon Hemming)