Gerard Chaliand said Colombo's military push was not the answer to the rebels' violent campaign for autonomy for minority Tamils in the island's north and east.
"I believe generally, terrorist organisations have legitimate reasons, mostly the majority who rule have a tendency to keep power to themselves," the former director of France's European Centre for the Study of Conflicts told delegates at an international counter-terrorism conference here.
"But no military solution can solve the problem by itself," he said.
Sri Lanka's ethnic conflict has claimed more than 60,000 lives since 1972 and despite a 2002 Norwegian-brokered truce, battles, aerial bombardments, suicide bombings and the massacre of civilians continue.
Nordic truce monitors have repeatedly said that the ceasefire holds only on paper.
Chaliand said the Liberation Tigers of Tamil Eelam (LTTE), led by their chief Velupillai Prabhakaran, remained one of the world's deadliest terror organisations, running their own air,