Rebels in South Sudan's volatile Jonglei state killed at least 41 people and wounded 46 others in a raid on three cattle camps on Sunday, a local official said.
Since breaking from Sudan in 2011, oil-producing South Sudan has struggled to assert control over remote territories awash with weapons after a 1983-2005 war with the north and torn by ethnic rivalries.
Dau Akoi, commissioner of Twic East, a county in Jonglei, said rebels loyal to former theology student David Yau Yau were believed to be behind the attack.
Yau Yau last year recruited armed youths antagonised by a government campaign to end tribal violence in Jonglei, which human rights groups say was marked by abuses by soldiers.
More than 1,500 people have been killed in Jonglei since independence, according to the United Nations. Yau Yau has refused President Salva Kiir's offer of amnesty.
Akoi said all the cattle were taken in the raid that killed 41 people and wounded 46.