By Tom Winter and Pete Williams, NBC News

(NBC) - Federal agents and local police in New Jersey and New York were investigating seven suspicious letters or packages sent to hotels and other locations near the site of Sunday's Super Bowl in East Rutherford, N.J. But federal officials told NBC News that one letter examined at an unidentified location was found to contain only baking soda.

"The Joint Terrorism Task Force and Hazard Materials units have responded to several locations that have received a suspicious letter and substance," the FBI said in a statement. "There are no reported injuries at this time, and the locations are being secured. This situation is being thoroughly investigated and more information will be provided when it becomes available."

FBI and New Jersey law enforcement sources told  NBC News that six of the packages were received in the north New Jersey area and one in Manhattan.

Authorities would not identify the sites that received the packages or describe why they were considered suspicious.