“The army has been conducting reconnaissance missions in South Sudan and they have a clear idea of where the children are,” Ethiopia’s Communications Minister Getachew Reda told AFP.

“We have sought approval of the government of South Sudan to conduct these operations, he added.

More than 200 people were killed and 102 children abducted by armed men from South Sudan in a cross-border raid into Ethiopia on April 15.

The assailants, armed with Kalashnikov rifles killed anyone who opposed them, according to witnesses. They also stole over 2,000 livestock.

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

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.

The Addis Ababa government had already said that its army was in pursuit of the attackers, but had not previously revealed that its troops crossed the border to hunt for them.

According to Ethiopia’s Fana radio, the army has already encircled the area where the abducted children are being detained and begun operations to rescue them.

Reda didn’t confirm these reports however.

Last week’s deadly raid has unleashed a wave of anger and boosted fears that the civil war raging in South Sudan could spill over the border.

Ethiopia has been heavily involved in the South Sudan peace process, partly because of the risk that the conflict could destabilise Gambella, 50 kilometres (30 miles) from the frontier.

After winning independence from Sudan in 2011, South Sudan descended into war two years later, setting off a cycle of retaliatory killings that have split the poverty-stricken country along ethnic lines.

Tens of thousands have been killed and over two million people forced to flee their homes.

Both the government and rebel sides have been accused of perpetrating ethnic massacres, recruiting and killing children and carrying out widespread rape, torture and forced displacement of populations to “cleanse” areas of their opponents.

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