Fierce fighting between Sri Lankan troops and ethnic Tamil separatists defending their last remaining enclave has left about 100 rebels dead in two days, the military said Sunday. The army has ousted the Tamil Tigers from most of their strongholds in an all-out offensive the government hopes will end the South Asian island's 25-year civil war. The rebel holdouts are confined to about 20 square miles (50 square kilometers) of jungle and beach near Mullaittivu on the northeastern coast along with tens of thousands of increasingly distressed civilians. Military spokesman Brig. Udaya Nanayakkara said Sunday that troops had killed about 100 rebels in a series of clashes in rebel-held territory since Friday, though he cautioned that only about 50 bodies were found. Troops also took casualties in three battles on the edge of the enclave, the army's Web site said. Nanayakkara would not say how many soldiers were killed or wounded. In one clash, more than 200 rebel fighters attacked security forces near Puthkkudiyirippu, the last rebel-held town, before dawn Friday, the Defense Ministry said. “Terrorist offensive waves were received with intense military counter attacks” that killed at least 30 guerrillas, the ministry said in a statement. Rebel officials could not be reached and battlefield details can't be verified independently because journalists are barred from the war zone. Concern is mounting for the fate of the civilians caught in the fighting. The government has rejected calls from international aid groups for a ceasefire, saying it is on the verge of victory, while the rebels have ruled out any mass evacuation of civilians - fueling suspicion they are using them as human shields. The UN says thousands of innocents have been killed or wounded in recent fighting and the survivors are dangerously short of food, drinking water, medical supplies and shelter. The Liberation Tigers of Tamil Eelam have fought since 1983 for an independent state for the Tamil minority, which suffered decades of marginalization at the hands of governments dominated by the Sinhalese majority. More than 70,000 people have been killed in the fighting.