The UN children's agency, UNICEF, said on Sunday it feared that hundreds of school boys were kidnapped in a mass abduction on February 15 and 16.

It had previously estimated that at least 89 boys were taken by an armed group in Wau Shilluk, a government-held area of South Sudan's oil-rich Upper Nile state.

"The organization now believes the number of children may be in the hundreds," UNICEF said.

The UN childrens' agency said it believed the group of armed abductors might have ties to the country's military.

The suspected kidnappers were from a "militia ... aligned with the government's SPLA (Sudan People's Liberation Army) forces," UNICEF said.

Mass recruitment campaign?

Witnesses to the abduction said the men surrounded the community and went door-to-door, taking away by force any boys thought to be over 12 years old.

UNICEF said the children were taken while doing their exams, and described the abductions as a mass recruitment operation.

South Sudan's conflict broke out a little over a year ago, in clashes between forces loyal to President Salva Kiir, and his former deputy, Riek Machar.

UNICEF said it believed that up to 12,000 children were being used as soldiers by both sides in South Sudan's ongoing civil war.

The latest kidnappings, however, were led by Johnson Oloni, a government-aligned militia chief. The news agency Associated Press said Kiir had summoned Oloni to the capital, Juba, over the allegations.

According to UNICEF, the SPLA has said the Johnson Oloni militia was outside its control.

Appeal to abductors

"We fear they are going from the classroom to the front line," said UNICEF’s representative in South Sudan, Jonathan Veitch.

"UNICEF appeals to Johnson Oloni to let those children go back to school and be with their families, immediately."

The ongoing South Sudanese conflict has left tens of thousands of people dead and displaced more than one million. South Sudan declared independence from Sudan in 2011.

jr/gsw (AP, AFP)