The United Nations is now estimating that hundreds of children were abducted by a militia in South Sudan after originally reporting that 89 were taken and forcibly recruited as child soldiers two weeks ago. UNICEF says it is no closer to locating the children than it was following the raids on Feb. 15 and Feb. 16, due to a “heavy militia presence” in the country's Upper Nile state.

Authorities believe a militia group formed by the native Shilluk people of South Sudan, under control of the Johnson Oloni militia and “aligned with” South Sudan’s military, the Sudanese People’s Liberation Army (SPLA), is behind the abductions. According to a UNICEF press release issued Saturday, the group is forcing the children to fight alongside the militia. The SPLA, meanwhile, said the Johnson Oloni militia “was outside its control,” according to the U.N.

“We fear they are going from the classroom to the front line,” said UNICEF’s representative in South Sudan, Jonathan Veitch, in a statment. “UNICEF appeals to Johnson Oloni to let those children go back to school and be with their families, immediately.”

The U.N. said it is “impossible to receive first-hand information” on the whereabouts of the missing children because of a heavy militia presence in Wau Shilluk, which is located in northern South Sudan. But the agency said reports indicate that the children aren’t being held together and that some of the children were allowed to go back into their villages to eat with their parents and go to school, but they were taken away again at night.

The child soldiers were reportedly being taken to Melut, in Upper Nile State, according to the U.N. Witnesses said they saw children in a training campaign in Wau Shilluk and that children as young as 12 years old were in Melut carrying guns, but not wearing military uniforms.

Veitch said those reports indicate that the abducted children were being sent to fight against rebels in Kaka about 45 minutes north of Melut.

Since its gained independence from Sudan in 2011, South Sudan has been embroiled in a civil war. About 12,000 child soldiers fought in the violence last year, according to the Independent.