An Ethiopian opposition party says that government forces have killed more than 80 people in the past four weeks in protests in the country's Oromia region.

The Ethiopian Federal Democratic Unity Forum, a coalition of four opposition parties, said the killings should be investigated.

The opposition party's charge comes after a report last week by Human Rights Watch that said government forces killed at least 75 people protesting the government plan to incorporate some rural areas into the capital city, Addis Ababa.

Violent clashes between protesters and security forces have spread across Ethiopia's Oromia Region, the biggest and most populous of Ethiopia's federal states. Oromo students charge the government's new master plan for Addis Ababa will take lands from their region and displace thousands of farmers.