Ethiopia has put a top opposition leader and his deputy under house arrest hours after clashes in which 22 died, an EU observer has reported.
Hailu Shawul is leader of the Coalition for Unity and Democracy, which denies being behind this week's student protests in the capital, Addis Ababa.
Ana Gomes, chief EU observer at last month's elections, condemned the deaths and protested to Ethiopia's government.
The ruling party has been accused of massive fraud at the polls.
Final results have not been announced three weeks after the polls as reports of the fraud are investigated.
EU observers have voiced concern over irregular vote counting and biased reports by the state-owned media.
Police fired live rounds to disperse stone-throwing protesters in the Mercato and Piazza markets in the city centre.
Injured protesters filled the city's Black Lion hospital while relatives crowded outside, many of them weeping.
Hundreds of students have been arrested this week for defying a protest ban.
Journalists reported seeing at least four bodies with bullet wounds in the head.