New York City will be under a security lock down as the tenth 9/11 anniversary approaches. City Police Commissioner Ray Kelly told CBS NEWS this week that he’s very concerned about potential  attacks timed to coincide with the memorials.

Although the city has not received specific threats, the NYPD will be on heightened alert for the 9/11 anniversary, he said.

'We have to be concerned,' Kelly told CBS. 'Osama bin Laden spoke about some event on September 11, 2011 twice in the last two years. The threat has not diminished. In some ways, you could postulate that it’s increased because of the revenge factor.'

Kelly says he shares President Obama's concern about so-called lone wolves operating independently, having been radicalized by what they have read online.

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The lower Manhattan police force will eventually rise to 670 next month, a much larger figure than any of the 76 precincts in the five boroughs.

For tourists planning to visit the new September 11 memorial,  airport-style screening will be in operation and their every move will be screened by hundreds of closed-circuit cameras as the new site opens publicly for the first time since 2001.