More than 200 people were killed and over 100 children abducted by armed men from South Sudan in a cross-border raid into Ethiopia, the country's leader said.

Ethiopian officials blame Murle tribesmen from South Sudan for a series of deadly attacks on Ethiopian villages in the western Gambella region on Friday.

"The atrocities committed by an armed Murle tribe from South Sudan claimed the lives of 208," Prime Minister Hailemariam Desalegn said on state television on Sunday evening, increasing the death toll from an earlier estimate of 140.

Hailemariam said "mothers and children" were among the dead and, "they also abducted 102 children."

The foreign ministry said over 2,000 livestock were also stolen.

The Murle, a tribe from South Sudan based in the eastern Jonglei region close to the Ethiopian border, often stage raids to steal cattle and abduct children but rarely on such a large or deadly scale.

"There had been abduction of children and raiding of cattle from Gambella through crossing the Ethiopian border. However, Friday's attack was massive" Hailemariam said.

"The Ethiopian defence force is taking measures against the attackers to free the abducted children without any precondition," he said, without specifying whether Ethiopian troops had crossed the border into South Sudan.

Friday's attacks targeted the Nuer tribe, one of the two main ethnic groups in South Sudan, who live on both sides of the border.

The western Ethiopian region of Gambella, which borders South Sudan, is also home to some 272,000 South Sudanese refugees who have fled the civil war that erupted in their country in December 2013.

The raid -- dubbed the "Gambella massacre" in the Ethiopian media -- reinforces long-standing fears that South Sudan's civil war since December 2013 would spill into Ethiopia.

The conflict has split South Sudan roughly along ethnic lines pitting the president's Dinka tribe against the rebel leader's Nuers. Ethiopia believes the raids are not linked to the ongoing conflict in South Sudan.

Located 50 kilometres (31 miles) from the South Sudanese border, Gambella is home to Ethiopian Nuers.

Local journalists have reported attackers carrying AK-47 assault rifles and killing anyone who resisted.