Opposition parties said Saturday that hundreds of their candidates and observers were arrested 12 hours before Ethiopians go to the polls.
Opposition leaders demanded their release.
Ethiopians were preparing Saturday for the most open election in the country's history, with foreign election observers spreading out across the country and a human rights group lodging a last-minute complaint.
According to an opposition leader, thousands of pre-marked ballots supporting the current government have already been circulated to voting stations.
Opposition leaders said they released the names of their observers on Friday, and the arrests began almost immediately in most districts.