United Nations, Apr 19 (IANS): A number of children have been killed in this week's fighting in South Sudan -- some in an attack on displaced civilians while others have been caught in the crossfire or died as a result of being recruited by armed groups and forces, the UN Children's Fund (Unicef) said Friday.

The exact number of children killed is not yet known but they were among the dozens of civilians injured and many killed by gunmen Thursday who attacked Internally Displaced Persons (IDPs), sheltering at the UN Protection of Civilians site, in the central South Sudanese town of Bor, Xinhua quoted the UN agency as saying.

"Utterly defenseless children were attacked in a place where they should have felt safe," said Jonathan Veitch, a Unicef representative in South Sudan. "The trauma for children under such circumstances is indescribable."

During intense fighting earlier this week in the oil hub of Bentiu, when hundreds of children fled for protection onto a UN base, others were observed carrying weapons, uniformed in military units, as well as undergoing military training. Unicef has credible reports that both sides to the conflict are recruiting children.

"This is fierce, brutal infantry fighting -- children must not be instruments of this conflict," said Veitch. "We talk of the long term damage done to children who are recruited, but right now the immediate threat is to their life."

"Those in positions of command and leadership have a duty to keep children out of harm's way and take all necessary measures to prevent children being part of armed groups and forces," he said.