More than 50 people were killed after Ethiopian police fired bullets and tear gas to disperse anti-government protesters at a religious festival in the country's Oromia region.
The incident occurred during the latest demonstration in an 11-month campaign by people in Oromia and Amhara against perceived government repression and the dominance of the minority Tigray ethnic group in one of Africa's fastest-growing economies.
The Oromia regional government said 52 people had been killed in the chaos on Sunday after thousands gathered at the Irreecha festival in Bishoftu, a town close to the capital Addis Ababa.
It blamed "evil acts masterminded by forces who are irresponsible" for the deaths and absolved the security forces of blame. But the Oromo Federalist Congress, an opposition group, said the toll was probably much higher: some activists pull it at several hundred.
People were reportedly killed both by the police and in a stampede after tear gas was dropped from a helicopter, according to Jawar Mohammed, who runs the US-Based Oromo Media Network.
Some reports said the protest had been peaceful while others said bottles and stones were thrown at the security forces.
Ethiopia is among Africa's most tightly-controlled countries. The government won every seat in parliament in the 2015 general election and keeps a firm grip on the economy, which has boomed thanks to well managed state-led industrialisation and urbanisation policies despite foreign investors being in effect banned in key sectors such as banking and telecoms.
However this leaves few outlets for dissent. The Oromo people, who live in a vast swath of central and southern Ethiopia, started protesting last November over government plans to expand Addis Ababa into their homeland.
The initiative was eventually shelved but the campaign evolved into a broader anti-government movement that spread to other areas, notably Amhara. The Amhar people make up about a quarter of Ethiopia's 100m population.
Hundreds of people have been killed in the authorities' response to the campaign, many of them children, according to rights groups.
The movement gained international attention when Feyisa Lilesa, an Oromo, made the movement's protest gesture by crossing his wrists above his head as he approached the finishing line to win the silver medal in the Rio Olympics marathon. He has since refused to return to Ethiopia.
Sunday's government statement said those responsible for the deaths "will face justice", without giving further details. Anti-government protesters say there has been widespread immunity so far for members of the security forces believed to have participated in the crackdown.
One western diplomat in Addis Ababa said Sunday's protest should send a clear signal to the government that "they need carrots as well as sticks" to deal with the demonstrators. "After 11 months it's clear that the Oromo and others are not going to give up and go away. A different approach is need to address their grievances."
Western governments view Ethiopia as a key partner both in combating terror groups, like al-Shabaab in neighbouring Somalia, and containing migration from east Africa towards Europe. Last month the EU, World Bank and UK announced a $500m programme to build two industrialisation zones in Ethiopia with 30 per cent of the 100,000 expected jobs reserved for refugees.