An estimated 140 people protesting against a planned expansion of Ethiopia’s capital into neighboring Oromia state have been killed by security forces over the last two months, Human Rights Watch (HRW) has said.

The international rights group said on Friday that Ethiopian forces had killed people and wounded many others in what it termed as “the biggest crisis to hit Ethiopia since the 2005 election violence”.

The government has only confirmed five deaths since the protest broke out in November.

In December, university students in Ethiopia’s largest regional state, Oromia, clashed with anti-riot police as they protest against a government plan to expand the area of Addis Ababa, the country’s capital city, into Oromia.

The state, which is on the outskirts of Addis Ababa, is inhabited by the Oromo tribe which has long been marginalized by the central government. The Oromos are Ethiopia’s largest ethnic group, comprising about 40 percent of the country’s 93 million people.

The government has accused Oromo protesters of links with terror groups and said elites from the ethnic community “who have influence over the the population” were stoking the riots.

Despite a government block on local media outlets from broadcasting the news, images of several injured students surfaced on social media, while hundreds of other protesters have reportedly been rounded up in a crackdown on those demonstrating against several state-led development projects.

HRW’s spokesman Felix Horne said this development was “a dangerous trajectory that could put Ethiopia’s long-term stability at risk.”