Thousands of people have been arrested across Ethiopia after violent clashes in which police killed 36 people, a New York-based human rights group reported Wednesday.
The political unrest prompted Britain on Wednesday to suspend a planned $54.1 million increase in aid to Ethiopia, one of the world's poorest countries.
Human Rights Watch said student activists and opposition supporters were rounded up in a crackdown after last week's fighting.
"Opposition rhetoric may well have contributed to last week's unrest, but the government must take responsibility for the conduct of its own security forces," said Georgette Gagnon, the group's deputy Africa director. "The security forces have killed dozens of protesters and arbitrarily detained thousands of people across the country."
Ethiopian federal police said some detainees were being held at Ziway detention facility, 90 miles south of the capital Addis Ababa, but they could not give exact numbers.
"I don't have the exact figure but some detainees are in Ziway because of these disturbances," deputy police commissioner Hassan Shauffa told The Associated Press. "I don't think there are hundreds, let alone thousands, arrested in the regions."
Police have released many detainees and will free more in coming days, a government official said on condition of anonymity because the statement related to internal security.
In the capital, police detained at least three members of the Ethiopian Human Rights Council earlier this week.
"We consider the arrest and detention of these EHRCO (Ethiopian Human Rights Council) staff part of the government's continuous attempt to paralyze its work, and if possible neutralize it altogether," the council said Wednesday.
Human Rights Watch said it had obtained reports of mass arrests of opposition Coalition for Unity and Democracy supporters in at least nine cities outside the capital in recent days.
Problems extend beyond capital city
While international attention has focused on events in Addis Ababa, opposition members and students in other cities are increasingly at risk of arbitrary arrest and torture," Gagnon said.
Many of the people arrested in earlier roundups had been released "but smaller-scale arrests targeting CUD supporters and student activists have continued unabated," she said.
Ethiopia's main opposition leader was freed from house arrest after the country's main political parties agreed to work together for peace after 10 days of political unrest.
CUD leader Hailu Shawel told the AP he was informed Tuesday that his house arrest was lifted after two days of talks mediated by the European Union.
"This is a breakthrough and should now get the political process back on track," said European Commission Ambassador Tim Clarke, who mediated the talks.
The agreement lays the groundwork for all political parties to play a role in investigating complaints over the elections. Although the three main political parties signed a nonviolence pact Friday, the deal foundered after the opposition imposed conditions they have now retracted.
Ethiopia's ruling party, which has pledged itself to democratic reform but shown authoritarian tendencies, claimed victory in last month's elections, based on provisional results. But parties have lodged complaints in 299 of the country's 527 constituencies.
The ensuing violence threatens to destabilize Ethiopia, which faces cyclical drought and widespread hunger. It also could strain Meles' dealings with the international community.
Britain's International Development Secretary Hilary Benn announced the suspension of new aid after meeting Meles. Benn said Meles committed to investigating the clashes and making the findings public.
"I am putting on hold the planned increase in direct budget support which we were looking at," Benn told reporters. "In my view, it is sensible to hold on to that to see how the situation develops."
He said the $108 million Britain already has given to Ethiopia would not be affected.
In Washington, the State Department called on the Ethiopian security forces and the opposition Tuesday to exercise restraint.