Ethiopian officials said on Saturday that gunmen from South Sudan had crossed the border, killed 140 people and abducted at least 39 children, according to Reuters News Agency.
Getachew Reda, Ethiopia's communications minister, said the attackers were members of South Sudan's Murle tribe. The attack took place on Friday in the Gambela region, which borders South Sudan. The region hosts over 284,000 South Sudanese refugees who fled the bloody civil war which began in 2013.
Reda said that Ethiopian military had crossed the border into South Sudan in pursuit of the attackers. "Ethiopian troops are pursuing the bandits inside South Sudan," Reda said. "Sixty of the assailants have been killed so far."
The gunmen had no relation to South Sudanese government troops or rebel forces who fought the government in Juba in a civil war that ended with a peace deal that was signed last year.
South Sudanese officials were not immediately available for comment.
Under pressure from regional powers, the United States, the United Nations, and other countries, South Sudan's feuding sides signed an initial peace deal in August and agreed to share ministerial positions in January.
Fighting broke out in December 2013, months after South Sudanese President Salva Kiir sacked his deputy Riek Machar as vice president, exacerbating a political dispute that reopened ethnic rifts between Kiir's Dinka ethnic group and Machar's Nuer.
Machar said last week he would return to the capital Juba on April 18 to form a transitional government with Kiir.
Ethiopia's Gambela region has a sizeable Nuer population as well.