Dozens of people died Sunday at a festival after security forces fired tear gas into a crowd during a political protest and provoked a stampede.
There is no official toll, with opposition leaders estimating at least 100 dead. A statement from the government has said only that there was a "loss of lives."
The Irreecha thanksgiving festival of Ethiopia's Oromo people takes place in October every year, at the conclusion of the rainy season, at a sacred lake in the town of Bishoftu, about 25 miles southeast of the capital, Addis Ababa.
The Oromo, Ethiopia's largest ethnic group, making up about a third of the population, have for the past year been protesting their marginalization and the confiscation of their land for factories.
Feyisa Lilesa, a silver medal winner at the Summer Games in August, is Oromo and called attention to his people's struggles when he crossed his arms in an X as he ran across the finish line in Rio de Janeiro.
That same gesture was flashed by thousands of Oromos in Bishoftu during the festival, which participants this year said was more overtly political than usual.
"I've been coming to this for years. There was always some small chanting, but I've never seen something like this. It was totally political," one witness said at the rally that turned into a stampede. He spoke on the condition of anonymity for fear of arrest.
Estimates of the number of people flocking to the town for the festival have been as high as 2 million, but there were probably about 10,000 people in a field facing a podium where government-aligned tribal elders and party leaders were giving speeches.
Authorities had tolerated the chants calling for "freedom and justice" and condemning the government and its Oromo political party throughout Saturday, but that ended Sunday morning.
"The crowd started moving toward the podium. I heard the sound of a tear-gas bomb, and I saw police throwing them at the crowd as well," the witness said.
He said he also heard a few warning shots fired by the Federal Police, whose members wear a distinctive blue-camouflage uniform.
People fled into the bushes behind the field, but they encountered a deep ravine, and it was here where many died, piling on top of each other in panic.
"I saw people mourning in there, some trying to pull out the survivors," said the witness, who was among those at the ravine. "I could see people saying: 'Help me out. There are a large number of people beneath me in the mud.' "
The government's statement about the incident described it as "planned violence" during the peaceful celebration of a cultural festival.
"Some forces were seen attempting to express the views of other political forces after controlling the podium and snatching the microphone," said the statement, promising to bring those responsible to justice.
Merera Gudina, chairman of the opposition Oromo Federalist Congress, said that at least 100 had died and that the problems started because the government packed the podium with its own speakers, angering the crowd.
"The government tried to control it, tried to take over the show," he said. "This goes down as one of the darkest days in modern Oromo history where the government is shooting live bullets and tear gas, leading to such chaos."
Ethiopia is made up of several different ethnic groups, and since the overthrow of the Marxist regime in 1991, the government has adopted a federal system ostensibly giving each ethnic region a measure of self-rule.
Critics, though, say that what is actually a very centralized system is dominated by the Tigrayan minority that overthrew the previous regime and makes up just 6 percent of the population.
Over the summer, the Amhara ethnic group, the country's second largest, began protesting, too. Typical complaints involve the corruption of local administrations and a lack of democratic recourse.
Government-allied parties won every seat in Parliament in the 2015 elections.
Thousands have been imprisoned over the past year, and Human Rights Watch estimates that at least 500 people have died when security forces opened fire on the various protests.
The United States has expressed concern over the protests and the use of violence in quashing them.
Another witness to the stampede expressed bafflement over the use of tear gas on a packed crowd.
"If they had just tolerated and left them, it would have been fine. They were moving to go, but then suddenly they started to fire, and this thing happened," he said, also speaking on the condition of anonymity for fear of reprisal.