By Aaron Maasho

ADDIS ABABA (Reuters) - An Ethiopian court has charged 23 South Sudanese refugees with carrying out the "gruesome" murder of 10 Ethiopian civilians using sticks and shovels at a refugee camp in the western part of the country last April.

The defendants were accused of planning the attacks in retaliation for a car accident in which two refugee children were killed inside Jewi Refugee Camp in Ethiopia's Gambella region.

The killings, which took place at the same camp, sparked unrest in the town, where some South Sudanese Nuer have been the victims of attacks by Ethiopian "highlanders" - a term used in the region for those who trace their origins to the central parts of the country.

"The perpetrators planned to attack in advance, in retaliation for the tragic car accident," said the charge sheet read out by prosecutors in Ethiopia's high court late on Monday.

"On April 21, they used sticks and shovels to carry out gruesome killings. The 10 victims were all innocent Ethiopian civilians who were only employed as construction workers at the site," it said, adding that some suspects were on the run.

The dead included two women. The trial will resume on Oct. 13.

Gambella, also home to an indigenous Nuer majority, hosts over 270,000 South Sudanese refugees who have fled the recurring cycle of violence in the world's youngest country since the outbreak of civil war in December 2013.

The killings came days after ethnic Murle gunmen from South Sudan carried out cross-border raids into Gambella, killing over 200 people and kidnapping nearly 110 children.

Violence has continued in South Sudan despite the signing of a peace deal that ended a civil war which largely pitted President Salva Kiir's Dinka ethnic group against rebel leader and former vice president Riek Machar's Nuer in August 2015.

The U.N. Security Council authorized an extra 4,000 troops for the capital Juba on Friday, in reaction to days of fierce fighting which raised fears of a slide back to full-scale war.

(Reporting by Aaron Maasho; Editing by Richard Balmforth)