UNITED NATIONS - The top U.N. official in Afghanistan Saturday called for a thorough investigation of reports that large numbers of civilians were killed during an international military operation in the far west of the country. Kai Eide, the Secretary-General's Special Representative, issued a statement in which he said he had learned late last night that civilians may have been killed during the operations, carried out by U.S.-led coalition forces, in Shindand district of Herat province. He stressed the importance of a thorough investigation to establish the facts "before we jump to any conclusions. The United Nations has always made clear that civilian casualties are unacceptable " they undermine the trust and confidence of the Afghan people." Eide said he had instructed the Herat office of the UN Assistance Mission in Afghanistan (UNAMA) to help provincial authorities to establish and verify the facts. "Any civilian casualty is one civilian casualty too many," he said. "And every effort that can be made must be made to ensure the safety and welfare of the civilian population where military operations are conducted."