Suspect Snapshots

The U.S. expelled two security guards at Iran's mission to the United Nations last week for activities "inconsistent with their official duties," a euphemism for spying. The State Department says the pair were caught videotaping New York City landmarks and sensitive infrastructure, including a key subway tunnel. And the event may not be an isolated one. Senior federal law-enforcement sources tell TIME it's just the latest in a spate of incidents of suspected "pre-operational surveillance" by people thought to have links to Middle Eastern extremist groups.

Individuals seen taking photos of landmarks and other potential targets are not usually arrested (it's not illegal), but U.S. officers check their pictures and enter their names in an interagency record base. On June 29, for example, a man claiming Swiss citizenship was questioned after he was seen photographing an oil refinery in Texas. Authorities examined the images and found pictures of nuclear-power plants in Ohio and Michigan. A senior official told TIME there have been two other incidents of suspected snooping at energy facilities in the past month.

Ports have been another site of suspicious activity. On June 24 at the Benicia Port terminal, 24 miles from the Golden Gate Bridge, a photographer fled as police approached him twice on the same day. A few days later, a Middle Eastern man was spotted training a camera on the terminal piers of New York City's Staten Island ferry. Law-enforcement sources have had reports of suspicious photography of ferries in California, Texas, Louisiana and Washington State. In yet another incident, a guard confronted three Middle Eastern men who were photographing and videotaping the Towne Square Mall in Boise, Idaho. A security guard said the three claimed to be "on holiday," but their pictures showed a survey of the mall, its stores, exits, corridors and support structures. Any or all of these incidents, of course, may have been innocent. But federal officials are reviewing them and urging local law-enforcement to be vigilant against a possible terrorist strike this summer or fall.

--By Adam Zagorin and Elaine Shannon