The attack took place on April 15 in the Horn of Africa nation's Gambela region which, alongside a neighboring province, hosts more than 284,000 South Sudanese refugees who fled conflict in their country.
By April 17 afternoon, the number had risen to "208 dead and 75 people wounded" from 140 a day earlier, government spokesman Getachew Reda told Reuters, adding the assailants had also abducted 108 children and taken 2,000 head of livestock.
"Ethiopian Defense Forces are taking measures. They are closing in on the attackers," he said.
Getachew did not give further details, but officials in Gambela said on April 16 Ethiopian troops had crossed the border in pursuit of the attackers.
Cross-border cattle raids have occurred in the same area in the past, often involving Murle tribesmen from South Sudan's Jonglei and Upper Nile regions - areas awash with weapons that share borders with Ethiopia.
Previous attacks, however, were smaller in scale.
The gunmen are not believed to have links with South Sudanese government troops or rebel forces who fought the government in Juba in a civil war that ended with a peace deal signed last year.
South Sudanese officials were not immediately available for comment.
Under pressure from neighboring states, the United States, the United Nations and other powers, South Sudan's feuding sides signed an initial peace deal in August and agreed to share out ministerial positions in January.