NEW YORK (AP) -- New York's mayor served notice Friday that his police department will do everything within its power to root out terrorists in the U.S., even if it means sending officers outside the city limits or placing law-abiding Muslims under scrutiny.
"We just cannot let our guard down again," Mayor Michael Bloomberg warned.
The mayor laid out his doctrine for keeping the city safe during his weekly radio show following a week of criticism of a secret police department effort to monitor mosques in several cities and keep files on Muslim student groups at colleges in Connecticut, New Jersey, Pennsylvania and upstate New York.
Several college administrators and politicians have complained that the intelligence-gathering -- exposed in a series of stories by The Associated Press -- pried too deeply into the lives of innocent people.
With about 1,000 officers dedicated to intelligence and counterterrorism, the New York Police Department has one of the most aggressive domestic intelligence operations in the U.S. Its methods have stirred debate in legal circles over whether it has crossed the line and violated the civil liberties of Muslims.
In perhaps his most vigorous defense yet of some of the NYPD's anti-terrorism efforts, Bloomberg said it is "legal," ''appropriate" and "constitutional" for police to keep a close eye on Muslim communities that terrorists might use as a base to strike the city. And he said investigators must pursue "leads and threats wherever they come from," even across state lines.
"It would just be naive to think we should stop following threats when they get to the border," Bloomberg said.
In the past few days, the department has come under fire from university officials and others, including the president of Yale University, after the AP revealed that police agents had monitored Muslim student groups around the Northeast and had sent an undercover agent on a whitewater rafting trip with some college students.
More criticism came from public officials in New Jersey after another AP report detailed a secret effort by the NYPD to photograph every mosque in Newark and catalog Muslim businesses.
That operation was an extension of a similar tracking effort within New York's city limits. Plainclothes officers swept through Muslim neighborhoods, photographing mosques and eavesdropping on businesses. Informants reported on what they heard inside mosques, including the sermons. Police monitored and kept files on Muslims who Americanized their names. They also infiltrated Muslim student groups.
Critics have said it isn't appropriate for the police to spy on citizens without reason to believe they committed a crime.
The American Civil Liberties Union issued a statement Friday accusing the NYPD of turning the city into a "surveillance state."
Faiza Patel, co-director of a civil rights program at the Brennan Center for Justice at New York University's law school, said guidelines in federal court rulings do not allow the department to hold on to files detailing the conversations of mosque worshippers "unless the information relates to potential terrorist or criminal activity."
Rep. Rush Holt, a New Jersey Democrat, questioned why the NYPD was assembling volumes of information on people who weren't suspected of breaking any laws.
"It's bad policing. It's profiling, fishing expeditions. They're looking around saying, 'Surely in this community there must be bad people. If we look long enough, we'll find them,'" Holt said.
Columbia University's president, Lee Bollinger, wrote an open letter Friday saying the NYPD shouldn't have been monitoring the websites of Muslim student groups at the school unless one of them had been suspected of a crime. Bollinger said the government's tactics could have a "chilling effect" on free speech and association.
"Such an intrusion into the normal, daily activities of our students raises deeply troubling questions that should concern us all," said Bollinger, a First Amendment scholar and former law school dean.
Anum Ahmed, an undergraduate student at New York University, said at a roundtable discussion Friday that she feels nervous now when doing simple things, like online research for her Arabic class.
"Even looking up words on Google Translate," she said. "I'm thinking, like, the NYPD is surveilling what I'm searching on the Internet."
Ahmed said she even feels frightened talking on the phone to her mother. "Sometimes I'm like, 'Should I be saying this out loud?" she said. "I don't feel like I'm protected. I'm being watched. And there's a big difference between the two."
Bloomberg said the NYPD would continue to do "everything that the law permits us to do" to detect terrorists operating in the U.S. before they have a chance to act. He warned of dire consequences if the city fails to detect plots.
"We are not going to repeat the mistakes that we made after the 1993 bombing," he said. "We cannot slack in our vigilance. The threat was real. The threat is real. The threat is not going away."
Newark Mayor Corey Booker was among several New Jersey officials who said they were surprised and concerned to learn that the NYPD had broadly monitored Muslims and mosques in that state.
Bloomberg acknowledged that Booker himself hadn't been briefed by the NYPD, but said the Newark police department had been informed. In any case, he said, it is "100 percent legal" for city police officers to operate in other states.
"You have to also remember an awful lot of the 9/11 hijackers stayed in New Jersey for extended periods of time, training, planning their attacks," Bloomberg said.
View the NYPD documents: www.ap.org/nypd