Prosecutors in Ethiopia have charged 131 jailed opposition leaders, reporters and aid workers with crimes ranging from treason to "genocide".
Some of the defendants are continuing their hunger strike
The charges relate to last month's protests over disputed May elections that saw at least 46 people killed.
Under Ethiopian law, some of the crimes carry the death penalty.
A visiting UK minister had talks with Prime Minister Meles Zenawi who assured him the arrests had been prompted by the threat of violence.
Minister for Africa Lord Triesman told the BBC he had had a "very useful exchange" on both the border situation with Eritrea and the political process in Ethiopia since the election.
But he added that the UK was reviewing development aid for Ethiopia worth £50 million ($88m).
He is also due to have talks with opposition figures and non-government organisations.
There have been repeated calls from the diplomatic community for political prisoners to be freed, BBC East Africa correspondent Karen Allen says.
The government in Addis Ababa has maintained the crimes are serious and those charged must be tried.
Ethiopia's Judge Adil Ahmed told a court in the capital on Friday that the charges against the 131 suspects included treason, genocide, conspiracy and causing an armed uprising.
At least 46 people died in a week of violence
About 55 defendants were present in the packed courtroom, including Berhanu Nega, a top leader of the opposition Coalition for Unity and Democracy (CUD), and human rights activist Mesfin Woldemariam.
Several of them have been on hunger strike for nearly three weeks to protest against their incarceration.
Prosecutors said all the defendants would face the same charges, and the case was adjourned until 21 December.
Some 8,000 people have been freed since the protests organised by the opposition, claiming that the 15 May elections were rigged.
There are no official figures for the number who remain in custody but diplomats say it is at least 3,000.
Mr Meles' Ethiopian People's Revolutionary Democratic Front won a majority in polls but the opposition gained many seats.
The opposition is made up of the two broad groupings - the CUD and the United Ethiopian Democratic Forces, which unlike the CUD, has taken up its parliamentary seats.