"I don't think it will be that long. Hopefully it could be by the (Sinhala and Tamil) New Year (in April)," he said.
The Sri Lankan government pulled out of a Norwegian-brokered truce a year ago, and the biggest offensive in decades of conflict has left the Tigers cornered in Mullaittivu after the fall of their political capital Kilinochchi earlier this month.
Military officials said eight divisions, or about 50,000 to 80,000 troops were advancing on the Tigers whose numbers were estimated by the military at the start of this year at 1,900.
Fonseka said his troops had advanced 17 kilometres (11 miles) towards the rebel-held Mullaittivu area in the past 17 days and that rebel resistance was crumbling faster than the military had anticipated.
This included at least 30 Tamil Tiger guerrillas