Police spokesman Emilio Kayima told dpa that the suspected perpetrators had been recently expelled from the Saint Bernard Secondary School in Rakai district.
An unknown number of the injured children were rushed to the hospital in the nearby town of Rakai, Kayima said.
Local broadcaster CBS Radio, however, placed the number of the dead at 20.
The exact circumstances of the fire, which had broken out around midnight, were still under investigation.
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