"We have always been ready for peace talks, but the Sri Lankan government has been always insisting on a military solution," he said.
The two sides have been battling for more than 25 years over the Tamil Tigers' demand for an independent state for minority Tamils in the north and east of the Indian Ocean island nation.
The military push deep into the separatists' heartland in recent months has forced the Tamil Tigers to retreat from vast areas they once controlled, and the government has said it expects to finish off the group in the coming months.
However, Balasingham Nadesan said the group did not believe it was facing imminent defeat.
"We have made several strategic withdrawals in order to save the lives of our people and maintain the strength of our forces. When the time and place is conducive, we will regain the land we have lost," he said.
Initial ceasefire
The two sides agreed to a truce in 2002 and held internationally brokered peace talks aimed at resolving the bloody conflict.
The talks stalled, however, and violence erupted again three years ago. The government officially pulled out of the ceasefire in January.
The government has said it would only consider new peace negotiations if the separatists agreed to disarm.
"For three decades we were trying to convince [Tigers leader Velupillai] Prabhakaran and his terror group to come to some sort of reasonable arrangement, but they failed," Keheliya Rambukwella, a cabinet minister, said.
If the group refuses to lay down its weapons, "we will not move an inch from our position."
More than 70,000 people have been killed in the conflict between the two sides.