South Sudan gains control of town where ethnic tensions flared, official says January 2, 2012 -- Updated 1635 GMT (0035 HKT) NEW: Medecins sans Frontieres is trying to reach 117 aid workers who fled Information minister: Some of the thousands who fled have started to return to Pibor Earlier, an official said roughly 4,000 reinforcements were being sent to Pibor The town had been under attack by fighters from a rival tribe Khartoum, Sudan (CNN) -- South Sudan's government has gained control of a remote town that had been under attack by fighters from a rival tribe, the nation's information minister said Monday. Some of the thousands who fled into the bush have begun to return to Pibor, said Barnaba Benjamin, South Sudan's minister of information and broadcasting. Earlier Monday, a military official said that roughly 4,000 army and police reinforcements were on the way to Pibor after weekend attacks. The United Nations also said it sent a battalion of peacekeepers to Pibor last week amid reports that members of the Lou Nuer tribe were marching toward the town, home to the Murle tribe, after attacking the village of Lukangol. Ethnic tensions in the South Sudan state of Jonglei have flared as tribes fight over grazing lands and water rights, disagreements that have dissolved into cattle raids and abduction of women and children. The fighters first struck Pibor on Saturday, attacking a portion that was out of the reach of U.N. peacekeepers, said Col. Philip Auger of the South Sudan army. Benjamin said there were no casualties and no direct confrontation between the two tribes there, because most of the Murle had fled when they heard the Lou Nuer were approaching. The nonprofit group Medecins sans Frontieres, also known as Doctors Without Borders, was still trying Monday to reach 117 of its 130 aid workers who fled into the bush along with the populations of Pibor and Lukangol before the attack, said Sarathy Rajendran, head of the group's South Sudan mission. Rajendran said the organization was afraid for its workers' safety and "very concerned" for the people of Pibor and Lukangol. "We believe tens of thousands are currently displaced without access to water, food and health care," he said. The situation is tense. We don't know what is happening on the ground, so we are monitoring the situation. The nonprofit's clinic in Lukangol was "burned and looted," spokeswoman Emily Linendoll said, adding that its Pibor clinic "has been targeted."