FILE - This Feb. 26, 1993 file photo shows the twin towers of the World Trade Center in New York City after an explosion earlier in the day which killed six. Some analysts say the U.S.'s conflict with factions of Islamist militants and terrorists dates back further than the autumn of 2001, citing such incidents as the 1993 bombing of the World Trade Center and the 1983 bombing that killed over 240 U.S. servicemen at a barracks in Lebanon. (AP Photo/Ron Frehm, File)