Eighty-eight Ethiopian children abducted in April by South Sudanese gunmen have been released and returned home, the UN children's agency Unicef said Thursday.

At least 216 people were killed and 136 children abducted in the cross-border raid into Ethiopia's south-western Gambella region on April 15.

"The majority of the children are between three and five years old. Many looked very distraught and dazed," said Sacha Westerbeek of Unicef Ethiopia. "They have seen people killed in front of their eyes. You can see the fear in the eyes."

Five of the rescued children are suffering from malnutrition, including a six-month-old baby who was fed cow's milk instead of breast milk after being abducted. The kidnapped children from the Nuer ethnic group were held by Murle communities and fed the traditional diet of milk and cow's blood during their abduction. Some were taken into Murle families and given Murle names.

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

The unprecedented nature of the April raid led the Ethiopian army to cross the border to look for the children after the attack, in which more than 3,000 livestock were also taken. Negotiations continue for the release of a further 58 children still being held captive.

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The release of all the children so far has been achieved through negotiation rather than force.

READ: 19 kidnapped Ethiopian children freed in South Sudan