Members of Ethiopia's largest ethnic group chanted and waved flags as they gathered for the first time to celebrate their thanksgiving festival in the capital - a city that prominent members of the group claim belongs to them.The annual Irreecha festival of the Oromo people marks the end of the rainy season and the start of the harvest season. It is traditionally held in the city of Bishoftu, located in the Oromia region some 50km southeast of the capital, Addis Ababa. Many Oromo leaders argue that Addis Ababa is part of their group's territory, meaning the decision to allow Irreecha celebrations there risked exacerbating ethnic tensions. But a concert on Friday night in the central Meskel Square and blessing ceremonies on Saturday morning appeared to have unfolded without major incident. Dawud Ibsa, leader of the opposition Oromo Liberation Front, a former rebel group, told AFP that Saturday's celebrations would be "very significant" for Oromos who believe their claims to Addis Ababa have not been respected. "This is our turn and a revival of what is taken from you," he said. Irreecha has already been a political flashpoint in recent years. In 2016, the use of tear gas and firearms by security forces sparked a stampede that killed dozens of people, some of whom drowned in a nearby lake. The government put the death toll at 55, though Human Rights Watch later said it could have been in the hundreds. The following year Irreecha turned into an anti-government protest. Last year's Irreecha - the first since Prime Minister Abiy Ahmed, himself an ethnic Oromo, came to power - was peaceful. The celebrations in Addis Ababa on Saturday will be followed by a larger event on Sunday in Bishoftu. State-affiliated Fana Broadcasting Corporate said Irreecha was expected to draw "millions of Oromos from all over the country as well as non-Oromo visitors from different parts of the country and other parts of the world".Abiy said in his Irreecha message that the festival was "a symbol of peace and unity", Fana said.Security forces were nonetheless on high alert. Federal police reported on Thursday that they had detained a number of people with weapons who were seeking to "disrupt" Irreecha. Security is expected to be tight in Addis Ababa all weekend, and roads in the city centre were closed on Saturday.