South Sudan's government has declared troubled Jonglei state a disaster area [Al Jazeera]

Dozens of people have been killed and three villages burned to the ground in South Sudan in an apparent tribal revenge attack, according to local officials.

Up to 400 men from the Murle ethnic group attacked the Lou Nuer villages in Uror county on Wednesday, an official in Jonglei state told The Associated Press on Friday.

Simon Hoth, a county commissioner, said 57 people had been killed and another 40 believed to have been abducted. He said 25 women and 23 children were among the dead, while another 52 people were left wounded.

"They have butchered these people," said Hoth, a member of the Lou Nuer. So far, there has been no independent verification of the figures provided by Hoth.

Murle fighters were accused of killing 22 in similar attacks in neighboring Akobo county on Sunday.

Retaliatory attacks

The Uror county was also the scene of a Murle attack in August which led to the deaths of an estimated 600 Lou Nuer.

Those attacks prompted a series of retaliatory raids by the Lou Nuer in Pibor county. One Murle official has said that 3,000 Murle died in those attacks.

Neither the central government nor the U.N. has confirmed that figure, but scores are feared to have died.

The state of Jonglei has been the site of on-going violence in the last three weeks and the government of the world's newest nation recently declared it a disaster area.

The United Nations mission in South Sudan estimates at least 60,000 people have been affected by the ongoing violence in Jonglei.