Border clashes between Ethiopia's Afar and Somali regions have killed at least 100 people, a regional official said on Tuesday, the latest outbreak of violence ahead of national elections in June.

Around 100 civilians were killed since clashes broke out on Friday and continued through Tuesday, Ahmed Humed, deputy police commissioner for the Afar region, told Reuters by phone. He blamed the violence on an attack by Somali regional forces.

Ali Bedel, a spokesperson for the Somali region, said 25 people had been killed on Friday and an “unknown number of civilians” died in a subsequent attack by the same forces on Tuesday.

Both sides deny having initiated the attacks and blame the other for the violence. Reuters could not verify whether the 25 deaths claimed by the Somali official were in addition to the 100 deaths or included in that figure.

Clashes along the border predate the six-month-old conflict in the north that has pitted the federal government against the former ruling party of the Tigray region.

Yet the violence has intensified just as Prime Minister Abiy Ahmed’s government is trying to assert control over Tigray - underscoring how the 2019 Nobel Peace Prize winner is struggling to keep the country together. The election is regarded as a litmus test for the country’s fragile unity, challenged by many newly resurgent regional and ethnically based parties.

"The Somali region special forces ... attacked the areas of Haruk and Gewane using heavy weapons including machinegun and rocket-propelled grenades. Children and women were killed while they were sleeping," Ahmed said.

In 2014 the boundary between the two states was redrawn by the federal government, then headed by a multi-ethnic ruling coalition, the Ethiopian People's Revolutionary Democratic Front (EPRDF). Three small towns were transferred to Afar from Somali, which has since tried to win them back.

As a result militias from the two eastern states have clashed before over their disputed boundaries. In October last year 27 people were killed in a wave of clashes over the border, with each side blaming the other.