The ex-cadre Krishnapillai Kalainesan alias Praba was taken into custody in Batticaloa city on Monday for interrogation, Xinhua news agency reported.
Praba is the third high profile former rebel cadre to be arrested by the TID recently.
Reports said Praba had been released in 2013 after being rehabilitated, following the end of the war.
His arrest comes as the government assured that any attempt by the Tamil Tiger rebels to regroup in Sri Lanka will be thwarted.
Government troops defeated the rebels in May 2009, ending a 30 year civil war in the island nation.
The UN estimates that at least 40,000 civilians were killed in the final stages of the war.