This has been pretty obvious for a few years, with these Iranian "diplomats" getting picked up on several occasions and then fleeing the country, but a leak from an NYPD briefing has acknowledged it's a serious concern, so it's in the news again.
New York: Targeted By Tehran?
March 5, 2007 issue - Increasing tensions between Washington and Tehran have revived New York Police Department concerns that Iranian agents may already have targeted the city for terror attacks. Such attacks could be aimed at bridges and tunnels, Jewish organizations and Wall Street, NYPD briefers told security execs last fall, according to a person with access to the briefing materials who asked for anonymity because of the sensitive subject matter.
NYPD officials have worried about possible Iranian-sponsored attacks since a series of incidents involving officials of the Iranian Mission to the United Nations. In November 2003, Ahmad Safari and Alireaza Safi, described as Iranian Mission "security" personnel, were detained by transit cops when they were seen videotaping subway tracks from Queens to Manhattan at 1:10 in the morning. The men later left New York. "We're concerned that Iranian agents were engaged in reconnaissance that might be used in an attack against New York City at some future date," Police Commissioner Raymond W. Kelly told NEWSWEEK. A spokesman for the Iranian Mission in New York said he was aware of the allegations but had no immediate comment.