The man known as "Colonel Karuna," who led an unprecedented split in the movement in 2004, says the Tigers will revert to guerrilla warfare after they lose control of the small enclave they still occupy.
"I think it will take at least another one to one-and-a-half years for the army to entirely clear the north of terrorists," Karuna said in an interview with AFP inside a heavily-guarded hideout in Colombo.
Following his defection, Karuna helped the Sri Lankan army to drive rebels out of the eastern district of Batticaloa, in what was one of the biggest military successes in 2007.
Troops have since moved north, taking vast swathes of land from the Liberation Tigers of Tamil Eelam (LTTE) and have cornered them in a small jungle patch along the northeast shoreline.
"The military is now equipped with high-tech gear. So when it came to the north, I shared insights with them on overall areas like civilians, ground realities, what areas were densely populated," he said.
Karuna -- a nom