Ethiopian authorities say they have now freed more than 8,200 people who were detained in clashes between security forces and opposition protesters earlier this month.
State-run media report the released detainees were cleared of being direct actors in the violence, in which at least 46 people were killed.
The government did not say how many remain in custody.
Last week, Prime Minister Meles Zenawi said a group of detained opposition leaders and journalists are to face treason charges for their alleged role in the violence.
The violence erupted during anti-government protests against alleged fraud in May parliamentary elections won by Ethiopia's ruling party.
In a statement Tuesday, the press freedom group Reporters without Borders asked United Nations Secretary-General Kofi Annan for "urgent mediation" in Ethiopia.
Some information for this report provided by AFP, AP and Reuters.