NAIROBI (AP) ― Red Cross volunteers are trying to reconnect 150 young children with their missing parents after tens of thousands of residents of South Sudan ran into the bush while fleeing a massive wave of tribe-on-tribe violence, an official said Tuesday.

Many of those parents, though, are feared to be dead.

Violence broke out late last month between two South Sudanese tribes in the town of Pibor, sending tens of thousands of residents into the surrounding countryside. A death toll is not known because officials cannot gain safe access to the region. One community leader believes the toll is in the hundreds.

Save The Children said Tuesday that up to 25,000 women and children fled the violence and are living in the bush. The U.N. reported last week that 6,000 armed men were marching on Pibor.

“Children in the area already live in continual fear of violence and are often abducted in raids. If fighting continues thousands more could be killed, maimed, abducted or recruited to fight,” the group said.

The U.N. Deputy Humanitarian Coordinator for South Sudan estimated Tuesday that the death toll could be in the hundreds.

Speaking via video link from South Sudan’s capital, Juba, Lise Grande said she saw five corpses outside of Pibor.

“The situation on the ground now, in humanitarian terms, is grim,” Grande said. “Because people fled town, they didn’t take anything with them. They’ve been in the bush for up to a week. They haven’t had food, they haven’t had access to clean water, in a number of cases their people are wounded.”

She said the South Sudan government had promised to reinforce troops with 3,000 infantry soldiers 800 police officers who were beginning to arrive.

David Gai, who works with the Red Cross in South Sudan, said the situation in Pibor has stabilized, and that several hundred people have returned to the town, but that about 150 children who were separated from their families in the mad scramble now cannot find their parents.

The youngest of the children is 6 months old, he said, and was found lying under a tree. Most are aged from 1 to 7 years old.

“It is not known if their parents are killed or lost during the attack. Our volunteers are trying to register them now,” Gai said, adding later: “What we assume now is that some of the parents are not alive, some of them are killed.”

Doctors Without Borders said Tuesday that two of its medical facilities were targeted during the violence and that the group had to suspend medical services in the region.

“Thousands of people have fled for their lives in Lekongole and Pibor in the last week and are now hiding in the bush, frightened for their lives,” said Parthesarathy Rajendran, the group’s head of mission in South Sudan. “They fled in haste and have no food or water, some of them doubtless carrying wounds or injuries, and now they are on their own, hiding, beyond the reach of humanitarian assistance.”

Doctors Without Borders said the village of Lekongole was razed to the ground, and that personnel who were in Pibor on Dec. 28 described it as a “ghost town.”

Columns of fighters from the Lou Nuer ethnic group marched into Pibor to target the Murle community, two tribes that have traded violent attacks over the last several years that have killed thousands. Much of the communities’ animosity stems from cattle raiding attacks.

U.N. Secretary-General Ban Ki-moon spoke with the South Sudan President Salva Kiir on Monday about the violence.

South Sudan fought a decades-long civil war with northern neighbor Sudan, a war that culminated in a 2005 peace deal that saw the partitioning of Sudan and the birth of South Sudan last July. The new border between the two countries remains tense, with sporadic cross-border attacks taking place. But the violence between the Lou Nuer and the Murle inside South Sudan is a reminder of the challenges the world’s newest country faces inside its own borders.

Mary Boyoi Gola, a representative of the Murle community on a team of peace negotiators, told the Associated Press she believes up to 20 of her family members were killed during the Pibor violence. Women and children who fled Pibor went to a river called the Kangen. Gola said she was told that the Lou Nuer carried out a massacre there, killing hundreds of Merle trapped by the river’s boundary.

Gai, of the Red Cross, said his group’s information is that 20,000 or more women and children fled to the river, because it is the only place to get drinking water. He said he has heard reports of mass violence similar to what Gola has been told, but that “it is very difficult for us to verify.”