Secretary-General Ban Ki-moon has sent his chief of staff to Sri Lanka for talks aimed at getting 100,000 civilians trapped by fighting between government forces and Tamil Tiger rebels out of the war zone, the UN said Thursday. UN associate spokesman Farhan Haq said chief of staff Vijay Nambiar, a former Indian ambassador, has already arrived in the capital, Colombo. He gave no details of his meetings. Haq said Ban was very disappointed that Tamil fighters refused to allow the civilians to leave during a 48-hour cease-fire on Monday and Tuesday. A rebel-allied Web site reported that Sri Lankan troops resumed their attacks on Wednesday and backed by helicopter gunships were pounding Tamil Tiger defenses in the northeast on Thursday. The civilians are stuck in a small "no-fire" zone on Sri Lanka's northeastern coast as government forces push the rebels - the Liberation Tigers of Tamil Eelam known as the LTTE - into an ever-smaller area, hoping to end the nation's 25-year civil war. Under intense international pressure, including from the UN, the government declared a unilateral cease-fire on Monday and Tuesday and urged civilians to leave the zone.