UNITED NATIONS (AP) - The United Nations and the New York City Fire Department have conducted their first joint exercise - tackling a mock explosion and fire in the 39-story U.N. headquarters building, a U.N. spokesman said Monday. In Sunday's drill, 26 vehicles and 150 firefighters responded to the hypothetical explosion on the 26th floor and a subsequent fire that included two possible casualties, spokesman Fred Eckhard said. The U.N. headquarters building overlooking Manhattan's East River was reported to be a terrorist target following the 1993 bombing of the World Trade Center. The New York landmark was evacuated after the...