JUBA (Reuters) - A tribal militia killed at least 43 people in South Sudan s Jonglei state, local officials said on Wednesday, extending a spate of tit-for-tat revenge killings.  Raiders from the Murle ethnic group killed 20 men, 22 women and one child, and injured 19 people in the village of Duk Payel on Tuesday, Jonglei Information Minister Jocab Akech Deng said.  The U.N. Office for the Coordination of Humanitarian Affairs said in a separate statement that among those killed were six staff members of local aid organizations. The killings are the latest chapter in a chain of revenge attacks, cattle raiding, and child abduction between the Murle and the Dinka Bor tribe.  The United Nations Mission in South Sudan (UNMISS) said that about 60 women and children had been abducted.  Oil-rich South Sudan dissolved into civil war in 2013 and is riven by rivalry between rebels, the military and tribal militias. More than a third of the country s 12 million population have fled their homes.  Kudumoch Nyakurono, the information minister of neighboring Boma state where the Murle are based, said his government was trying to find the culprits.  There are some villages which were attacked by some youth from Murle in Pibor,  said Nyakurono.    The government of Boma state has condemned this attack and we have sent commissioners and representatives from here to go and find out which village has organized this attack so that we can bring them to justice.   UNMISS said it was sending a peacekeeping patrol and human rights monitors to the area of the attack.  UNMISS deplores any incidents in which innocent civilians are killed. The mission will continue to support reconciliation efforts on the ground between communities to ease tensions and end the cycle of revenge,  said UNMISS spokesman Daniel Dickinson.  