A police officer of the New York Police Department (NYPD) stands guard outside a subway station in New York, the United States, March 29, 2010. New York City stepped up security as a precaution Monday following the suicide bombings in Moscow's subway system, sending more police into rail and subway stations. [Xinhua]

Police officers of the New York Police Department (NYPD) stand guard outside the Grand Central Station in New York, the United States, March 29, 2010. New York City stepped up security as a precaution Monday following the suicide bombings in Moscow's subway system, sending more police into rail and subway stations. [Xinhua]