Ethiopia's government has denied accusations that the conviction of 38 opposition leaders was intended to stifle political dissent.
The opposition blames the violence on the security forces
Government spokesman Bereket Simon told the BBC the court was independent and had based its verdict on hard evidence.
But an opposition lawyer said the suddenness of the verdict exposed the trial as a sham and mockery of justice.
The 38 were found guilty of links to 2005 protests against alleged poll-rigging, in which 193 people died.
Sentencing is next month and they could face the death penalty, says the BBC's Elizabeth Blunt in Ethiopia.
The charges ranged from armed rebellion to "outrage against the constitution".
Mr Simon said that legal, peaceful dissent was permissible but not "trying to overthrow the legitimate government by the use of force".
Hundreds of thousands took part in demonstrations complaining of fraud and vote-rigging by Prime Minister Meles Zenawi's government in the 2005 polls.
Most of the dead were protesters killed by security forces but Mr Simon pointed out that policemen had also died.
An independent inquiry carried out by an Ethiopian judge concluded that the police had used excessive force.
He went on to accuse them of carrying out a massacre. The judge later fled Ethiopia, saying he had been put under pressure to change his findings and had received death threats.
The Coalition for Unity and Democracy leaders refuse to recognise the court and did not present evidence in their defence.
The judge said that because they had failed to defend themselves he had no option but to find them guilty.
Andargachew Tsege, convicted in absentia as he is in exile in London, told the BBC he fears that his colleagues could be sentenced to "the most extreme" sentence.
"This government... has no notion of the implications of its actions - it's very vindictive, it has no sense of the sanctity of law, with all the various atrocities it has committed," he said.
The government points out that it introduced multi-party elections to Ethiopia after years of military rule.
In the elections, the opposition made huge gains but says it was cheated out of victory.
Two months ago, a judge threw out controversial charges of attempted genocide and treason against another 111 people arrested after the election protests.
The violence and the charges of election fraud have tarnished Mr Meles' image as a favourite of Western donors and one of a new wave of reforming African leaders.