WASHINGTON (AP) -- U.S. officials say the Obama administration is investigating whether the assault on the U.S. consulate in Libya was a planned terrorist strike to mark the anniversary of 9/11, and not a spontaneous mob enraged over a anti-Islamic YouTube video

President Barack Obama vowed in a Rose Garden address that the U.S. would "work with the Libyan government to bring to justice" to those who killed Ambassador Chris Stevens and three other American personnel. Intelligence officials said the attack on the Benghazi consulate was too coordinated or professional to be spontaneous, according to a U.S. counterterrorism official.

The official spoke on condition of anonymity because he was not authorized to discuss the incident publicly.