Ethiopia began three days of mourning on Monday for 52 people killed in a stampede after police clashed with protesters, the latest bloody episode in a wave of anger against the authoritarian government. Members of the country's largest ethnic group, the Oromo, had gathered on Sunday in the town of Bishoftu, some 50 km from Addis Ababa for a religious festival to mark the end of the rainy season. However political grievances took over, with Oromo protesters chanting anti-government slogans and crossing their wrists above their heads, a gesture that has become a symbol of protest against a government considered among the most repressive in Africa. Chaos erupted after police charged stone-throwing protesters and fired tear gas, triggering a stampede, according to a photographer on the scene. The regional government said in a statement that 52 people had died after panic swept through the crowd of tens of thousands of people, with some festival-goers falling into a deep ravine. Merera Gudina, chairman of the opposition Oromo Federalist Congress, said he believed there had been many more fatalities than the number officially announced. "Bodies are being collected by the government. But what I hear from people on the ground is that the number of dead is more than 100," said Gudina. On Monday the national flag was being flown at half-mast in government institutions and regular radio programs were replaced with music as the Horn of Africa nation mourned those killed. The regional government blamed "irresponsible forces" for the disaster. "The annual Irreecha festival has been disrupted due to a violence created by some groups... Loss of lives has occurred due to a stampede," said a government statement. Demonstrations against Prime Minister Hailemariam Desalegn's government first began in November 2015 over a government plan to expand the boundaries of Addis Ababa into the Oromia region. That project was binned, however a brutal crackdown on the protests kindled simmering anger against iron-fisted leaders who largely hail from the northern Tigray region and represent less than 10 percent of the population. "For the last 25 years the Oromo people have been marginalized in many things. Today we come together as one to chant for our freedom," said one of the people at the festival, Habte Bulcha. The protests in Oromia spread to the northern Amhara region, and international rights groups estimate at least 500 demonstrators have been killed and hundreds injured over the past 10 months. Together, Oromos and Amharas make up 60 percent of the population of Ethiopia. "This government is a dictatorship, there is no equality or freedom of speech. There is only TPLF. That's why we must protest today," said activist Mohamed Jafar on Sunday, referring to the Tigrayan People's Liberation Front. In 1991 the TPLF, then a rebel group, overthrew dictator Mengistu Haile Mariam, and now, as a political party stands accused of monopolizing power and keeping a stranglehold over the media. The West has largely avoided direct criticism of the country's rights record because Ethiopia is credited with beating back Al-Qaeda-affiliated Al-Shabab militants in Somalia. Oromo activists have called for "five days of rage" to protest the deaths.