While there is no specific threat against New York ahead of the Thursday commemoration, the rising power of disparate militant groups around the world presents the most complex terrorism danger since the twin towers were destroyed, New York intelligence officials said this week.
"It is layer upon layer upon layer, not all coming from the same place or ideology," said John Miller, the New York Police Department's deputy commissioner of intelligence and counterterrorism.
"When you look at the level of sophistication, the amount of slickness applied to their video production, the amount of thought that goes into creating a narrative," he said, "They're doing the same kind of thing as we've seen in commercial publishing or in the ad industry."
New York remains the top target, and that makes preparing for big events, including the US Open tennis tournament, the United Nations General Assembly and the September 11 commemoration, that much more critical, officials said.
New York Police Commissioner William Bratton said the department is prepared.
"We will, as always, ramp up intelligence gathering and visibility," Bratton said.