Factbox: Ethiopia's main ethnic groups

Here are some key facts about the main ethnic groups in Ethiopia, where diplomatic sources reported heavy fighting between federal and local forces in the northern Tigray region on Wednesday.

Ethiopia sends army into Tigray region, heavy fighting reported

Clashes between ethnic groups have become a major challenge to the government of the diverse country, which took its present form from territorial expansions of the 19th century:

Tigrayans - Tigrayans account for just 5% of the population but dominated politics and the security forces after Tigrayan rebels under Meles Zenawi toppled Marxist military leader Mengistu Haile Mariam in 1991.

Tigrayan leaders left the national ruling coalition after Prime Minister Abiy Ahmed was appointed in 2018. Some leaders have accused him of persecuting Tigrayans.

Tigray is the northernmost of Ethiopia's nine regions.

Oromos - They make up 35% of Ethiopia's 110 million people but have not held power in its modern history and have long complained of political exclusion.

A government plan to expand the capital using Oromo farmland in 2015 triggered three years of protests and bloody repression that eventually forced the prime minister's resignation and Abiy's appointment.

Although Abiy has rolled out greater freedoms nationwide, parts of western and southern Oromiya are under federal military control and Amnesty International has documented killings and abuse. Gunmen killed 32 people and torched more than 20 houses on Sunday, a regional administrator said.

Abiy is the first modern Ethiopian leader who is Oromo, but some Oromo figures say he has pushed his new pan-Ethiopian Prosperity Party at the expense of Oromo interests.

Amharas - Amharas were the traditional rulers under the era of Ethiopian monarchy that ended with the Soviet-backed overthrow of Emperor Haile Selassie in 1974.

Ethiopia's second largest ethnic group, with at least 20 million people, the Amhara claim they are increasingly politically marginalised.

Amharas hail from the northern and central highlands.

SNNPR - The Southern Nations, Nationalities and People's Region, located in the southwest abutting Kenya and South Sudan, is home to more than 40 ethnic groups.

Somalis - The dry and arid Somali region, also known as the Ogaden, occupies the eastern third of the country and is home to 6 million people.

It has a history of separatist rebellion against Addis Ababa, fuelled in large part by resentment at its low level of development.