Authorities have interviewed at least 13 people since 2005 with ties to Iran's government who were seen taking pictures of city landmarks, a senior NYPD official said Wednesday.

Police consider these instances to be pre-operational surveillance, bolstering their concerns that Iran or its proxy terrorist group could be prepared to strike inside the United States, if provoked by escalating tensions between the two countries.

Mitchell Silber, the NYPD's director of intelligence analysis, told Congress that the city's international significance as a terror target and its large Jewish population make it a likely place for Iran and Hezbollah to strike. Silber testified before the House Homeland Security Committee in Washington about the potential threat. Much of what Silber said echoed his previous statements on the potential threat, but he offered new details Wednesday about past activities in the city.

In May 2005, Silber said, tips led the NYPD to six people on a sightseeing cruise who were taking pictures and movies of such landmarks as the Brooklyn Bridge. In September 2008, police interviewed three people taking pictures of railroad tracks.

And in September 2010, federal air marshals saw four people taking pictures and videos at a city heliport. Interviews with law enforcement revealed that all were associated with the Iranian government, but they were ultimately released and never charged, Silber said.

U.S. officials long have worried that Iran would use Hezbollah to carry out attacks inside the United States. And Iran was accused in a disrupted plot to assassinate the Saudi ambassador to the United States here last year, a plan interpreted in the U.S. intelligence community as a clear message that Iran is not afraid to carry out an attack inside this country.

But government officials have said there are no known or specific threats indicating Iranian plans to attack inside the United States.

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