COLOMBO (AFP) - Sri Lanka Sunday rejected fresh calls for a ceasefire with Tamil Tigers rebels as security forces hit stiff resistance in their efforts to secure final victory in the island's ethnic conflict. 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 Tamils in southern India. Mukherjee said Colombo should consider a truce offered by the LTTE last week, although the guerrillas refused to lay down their arms as demanded by several countries including the US. "The government of Sri Lanka should seize the opportunity presented by the offer (of the Tigers) to bring about a pause in the hostilities," Mukherjee said. Sri Lanka's military leaders have consistently rejected truce calls, saying that the Tigers were on the verge of complete defeat. The state-run Sunday Observer newspaper said government forces faced stiff resistance from the rebels, who have been encircled in a 50 square kilometre (19 square mile) area in the district of Mullaittivu. The LTTE was fighting "tooth and nail" to defend their final stronghold of Puthukkudiriruppu, the Observer said. "The troops are witnessing the fiercest battles they have ever faced in the battle front these days in Puthukkudiriruppu," the paper said, adding that troops were still making progress towards the centre of the small town. Security forces entered the town's outskirts Friday, but have faced 600 rebel fighters, the report said, without giving casualty figures. The defence ministry said that security forces seized a 1.5-kilometre (one-mile) stretch of rebel bunkers east of Puthukkudiriruppu after heavy fighting Saturday. At least 22 guerrillas were killed in two days of fighting, the ministry said. The LTTE did not comment on the latest clashes.