Secretary-General Kofi Annan warned Eritrea on Monday that if it continues to impede U.N. peacekeeping operations the United Nations may pull its troops out of a buffer zone separating the Eritrean and Ethiopian armies, AP reported. Eritrea informed the United Nations that it was banning helicopter flights by U.N. peacekeepers in its airspace in the zone starting Oct. 5. It then banned U.N. patrol vehicles from operating at night on its side of the 1,000-kilometer (620-mile) Temporary Security Zone. The zone was established after a December 2000 peace agreement ending a 2 1/2-year border war between the Horn of Africa neighbors. The deal provided for the formation of an independent commission to rule on the position of the disputed border, but Ethiopia refused to accept the decision issued in April 2002 that awarded the disputed town of Badme to Eritrea. Annan told reporters the United Nations still has not been able to get any explanation from the Eritrean government for the bans on helicopters or night vehicle operations. «Obviously, we need all our tools _ helicopters, trucks, communications to operate,» he said. «We are placed in a situation where the government has not been cooperating and has limited the movement of our troops.» Annan said the United Nations has begun regrouping U.N. troops who were isolated «and positioning ourselves in a manner that protects the men.» The U.N. Mission in Ethiopia and Eritrea announced Monday that peacekeepers and military observers were pulling out of 18 isolated posts in the buffer zone and were being sent to strengthen operations at other positions. The U.N. has 22 other posts in the zone.