The United Nations says it is gravely concerned about thousands of children Uganda says have been abandoned in southern Sudan by a rebel group. Uganda began a military offensive last month in southern Sudan. Ugandan officials say it is an effort to destroy the rebel Lord's Resistance Army and free the children it abducted.

The U.N. Children's Fund estimates that during the past 10 years, the rebels kidnapped about 10,000 children from Northern Uganda and brought them to their camp in southern Sudan.

UNICEF says the children have been subjected to unthinkable abuse. It says they have been forced to serve as soldiers, porters, and sex slaves.

UNICEF Spokesman, Marc Vergara says the renewed conflict could endanger thousands of their lives.

"But, of course, for many of the children technically are not children anymore because they were kidnapped, some of them, 10 years ago," he said. "So, some of them are now young adults. In a way they also meet the targets for the army and the new situation that we have is that, of course, there is talk of children being released or abandoned and no one really knows where they are. So, we are really concerned about that."

Mr. Vergara says UNICEF is in touch with both the Ugandan and Sudanese governments. But, he says they say they do not know the whereabouts of the children.

"We are still waiting," Mr. Vergara said. "In fact, we have no news, no indication that children were in fact released or abandoned by the LRA anywhere. If that does happen, of course, that is what we want. We will be ready to work with the usual NGO [non-governmental organization] partners and take them back to their homes. But, at the moment, there is no sign of any child being found, released, abandoned or whatever. We have no news whatsoever from the field."

If and when the children are found, he says the agency will do whatever it can to protect them and reunite them with their families.