Foreign Secretary Palitha Kohona said any ceasefire would be unnecessary if the Tigers accepted international appeals to surrender.
"When the Tigers lay down arms, there will be no fighting.
The fire will automatically cease," Kohona told AFP.
Kohona was responding to calls from neighbouring India for a halt in the fighting in Sri Lanka's northeast, where the Liberation Tigers of Tamil Eelam (LTTE) have been cornered after two years of intense fighting.
Concern has mounted for the safety of an estimated 70,000 civilians trapped in the war zone, with the UN accusing the Tigers of forcibly holding civilians as "human shields."
"India views with grave concern the humanitarian crisis that is building up with every passing day in Sri Lanka," Indian Foreign Minister Pranab Mukherjee said in a statement late Saturday.
Indian politicians, facing a general election shortly, are under pressure to consider the welfare of Sri Lanka's Tamils who share close links with 60 million Tamil