Newark Mayor Cory Booker said he was unaware the NYPD surveillance program was building secret files on mosques in the city. REUTERS

New York City Police Department officers ventured out of their jurisdiction to monitor Muslims in Long Island and in Newark, New Jersey as part of a sweeping program to monitor and gather information on Muslims, The Associated Press reported.

Police officers compiled information on the locations of mosques in Newark and dispatched undercover officers to listen to conversations at Muslim businesses, producing a document that the AP described as a guide to Newark's Muslims.

Newark's police chief at the time told the AP that NYPD officers notified him when they were entering the city, but Newark's current mayor, Cory Booker, said he was unaware of the Muslim surveillance operation.

Wow, Booker reportedly said when the report's contents were described to him. This raises a number of concerns. It's just very, very sobering.

Booker told the AP his office has launched an investigation, citing a need to get to the bottom of this.

The report is the latest in a series of articles illuminating the NYPD's post-Sept. 11 push to collect data on Muslims, even in the absence of evidence suggesting a link to any wrongdoing.

With the help of a retired Central Intelligence Agency veteran, the NYPD formed a Demographics Units that fanned out to neighborhoods with high concentrations of Muslims and gathered information at mosques and businesses.

The former CIA official, David Cohen, convinced a judge to ease a rule that had prohibited officers from monitoring people unless there was sufficient evidence of criminal activity. After the AP story broke, the CIA opened an investigation.

Earlier this week, the AP reported that NYPD officers had infiltrated Muslim student groups at New York City schools while tracking the online activities of Muslim students across the Northeast.

New York City Mayor Michael Bloomberg defended the program, saying it was necessary.

We have to keep this country safe, Bloomberg told reporters on Tuesday. This is a dangerous place. Make no mistake about it.