Joanna van Gerten, Unicef's Sri Lankan representative, said the team was 'horrified' by the carnage.
'These were children from surrounding schools in the area who were brought there for a two-day training workshop on first aid, by whom we don't know yet,' she said.
Van Gerten said the Unicef team found more than 100 children, mostly girls aged between 16 to 19, being treated for various injuries. 'Most of the children we saw in the hospital had head injuries, shrapnel injuries,' she added.
The LTTE said it was observing a day of mourning for the children on Tuesday.