In another case, in July 1990, Karuna's forces stopped a convoy of Muslims traveling in eastern Batticaloa district and executed about 75 people, including women and children.
In August 1990 Karuna's forces killed more than 200 civilians in two incidents in Batticaloa district.
The LTTE widely recruited and used children as soldiers, which Human Rights Watch documented in a 2004 report.
Karuna's forces played a prominent role, routinely visiting Tamil homes to tell parents to provide a child for "the movement".
The LTTE harassed and threatened families that resisted, and boys and girls were abducted from their homes at night or while walking to school, Human Rights Watch said.
After Karuna broke away from the LTTE, his forces continued to operate with the complicity of the Sri Lankan security forces.
The Karuna group, as it was known, abducted children for use as soldiers in Sri Lanka's eastern districts, taking boys from their homes, work places, temples, playgrounds, public roads, camps for the internally displaced, and even weddings.
The Karuna group eventually joined forces with the Sri Lankan security forces and helped push back the LTTE's stronghold in the east. After that, Karuna entered politics.
He has been a MP since 2008. His party is part of the coalition of the governing United People's Freedom Alliance. He is currently the deputy minister for resettlement.
"Karuna has enjoyed immunity for some of the worst atrocities committed during Sri Lanka's long conflict," Adams said.
"His threat to initiate investigations against a political party is a cynical gesture aimed at silencing the opposition while denying his own responsibility for war crimes."
