Sri Lankan forces captured the Tamil Tigers' biggest sea base Thursday, as the government rejected calls for a ceasefire to allow civilians to flee, saying the rebels' “last moment” is near. Prime Minister Ratnasiri Wickremanayake told Parliament that the government will only accept an unconditional surrender by the Tamil Tigers, who are facing imminent defeat after a fruitless 25-year war for a separate Tamil homeland. The Sri Lankan government offered an amnesty to Tamil Tiger rebels who surrender, but rejected international appeals for ceasefire talks and vowed to crush those who fight on. Wickremanayake said some rebels were ready to lay down their arms as they face imminent defeat in their decades-long battle for an independent ethnic Tamil homeland. “It is a wise decision and we are ready to welcome them,” Wickremanayake said. The government at the same time rejected international calls for negotiations to end the fighting, which has triggered global concern for the tens of thousands of civilians caught up in the war. UN Secretary General Ban Ki-moon telephoned President Mahinda Rajapakse Thursday to discuss the plight of civilians trapped by the fighting and was assured that they would not be harassed, a government statement said. Some 70,000 people have died in the conflict. Hundreds of civilians are reported to have been killed in the latest round of fighting as the government presses ahead to annihilate the rebels. “Our forces have now surrounded the last stronghold of the terrorists. Our troops are challenging the Tigers waiting in front of their den,” Wickremanayake told Parliament.“The last moment of Tigers will be painful as well as decisive,” he said. The statement effectively rejected a call by the US, Britain and Canada for both sides to cease fire to allow civilians and the wounded to leave the area. After a string of victories over the rebels, the military has squeezed the Tamil Tigers into a 30-square-mile (85-square-kilometer) sliver of coastal land. In another victory, troops overran the insurgents' sea base in Chalai, Nanayakkara, the military spokesman, said. The seizure cuts off their main supply point as Chalai was used to receive arms and fuel from other countries through a widespread smuggling network. Nanayakkara said the rebels still retain some capability to launch naval suicide missions from small bases along the coast. But for now, the rebels are fighting a last-gasp battle for survival, bearing the brunt of a daily barrage of artillery. The United Nations and other aid agencies say some 250,000 civilians are trapped in the war zone along with the rebels. Military spokesman Brig. Udaya Nanayakkara said 1,282 civilians crossed over from the rebel area to government land on Wednesday and Thursday.