WASHINGTON – The heavily armed extremists who laid siege to the U.S. Consulate in Libya used military-style tactics that may have steered Americans toward a waiting ambush, U.S. officials said Friday as they pieced together details about how the compound was overrun.

U.S. intelligence indicates that more than 50 people, many of them masked, were responsible for the Sept. 11 assault on the U.S. diplomatic mission in Benghazi. Gun trucks provided added firepower. The attackers set up a perimeter, controlling access in and out of the compound. A first wave of attacks sent the Americans fleeing to a fallback building, where a second group of extremists beset them with precise mortar fire.

Intelligence reports were still coming in, but officials told The Associated Press that what may have initially seemed like a protest over an anti-Islam movie that had spun out of control now showed the hallmarks of a more sophisticated operation.