An opposition party has accused the Ethiopian government of beating, abducting and illegally detaining more than 150 of its members during July and September this year.
In a 39-page report launched on Thursday, the Unity for Democracy and Justice (UDJ) detailed what it said were "gruesome rights violations" committed against its supporters and members.
"One hundred and fifty members and supporters of the party have been subjected to severe beatings, illegal detentions and abductions by the police and security officials," Negasso Gidada, the party chairman, told reporters.
"We are asking the government to stop these human rights violations and take those responsible to justice," said Negasso, who served as the country's president from 1995 to 2001, before joining the opposition.
A government spokesman declined to comment saying it had yet to receive the report.
Earlier this month, Human Rights Watch said many former detainees - including politicians, journalists and alleged supporters of opposition groups - were slapped, kicked and beaten with sticks and gun butts during investigations at Addis Ababa's Federal Police Crime Investigation Sector, known as Maekalawi.
Ethiopia intensified its clampdown on peaceful dissent after the disputed 2005 election, the New York-based watchdog said.
At the time, the polls ended in violence, killing about 200 people.
Opposition candidates won 174 seats, but many did not take them up, saying the vote was rigged.
In an interview with Reuters this month, Prime Minister Hailemariam Desalegn said the government was not to blame for the opposition's poor showing.
He has also accused some opposition party members of collaborating with rebel groups the government had previously labelled as terrorist organisations.
But UDJ's leaders deny any links with the outlawed rebel groups, and warn the government that "stifling" dissent may encourage violence in the country.
"We are not requesting anything from the government side, we are requesting a level playing ground," Girma Seifu, a senior UDJ official and the sole opposition politician in Ethiopia's 547-seat parliament.
The Horn of Africa country has won international plaudits for delivering double-digit growth for much of the past decade, but rights groups often accuse the government of using state institutions to stifle dissent and silence political opposition.