NEW YORK (WCBS 880) – The NYPD is strengthening its safety net around the city as the 9/11 anniversary approaches and the city’s top cop says he’s very concerned about an attack timed to coincide with the memorials.

LISTEN: WCBS 880′s Marla Diamond reports

Police Commissioner Ray Kelly says the city has not received any specific threats, but is on heightened alert for the 9/11 anniversary.

“We have to be concerned,” Kelly said. “Osama bin Laden spoke about some event on September 11, 2011 twice in the last two years.”

Kelly says bin Laden’s death is not a game changer.

“The threat has not diminished. In some ways, you could postulate that it’s increased because of the revenge factor,” said Kelly.

Kelly says some of the avengers may be so-called lone wolves, radicallized by what they read online.

President Barack Obama has also said a “lone wolf” terror attack in the U.S. is more likely than a major coordinated effort like the September 11 attacks.

Security in lower Manhattan has also been a concern, especially around the September 11 Memorial and Museum.

The lower Manhattan force will eventually rise to 670 — larger than any of the 76 precincts in the five boroughs and entire departments across the country.

The thousands of visitors who will come to the September 11 memorial after it opens this fall will endure airport-style screening and be watched by hundreds of closed-circuit cameras as part of the attack site opens publicly for the first time since 2001.

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