MILWAUKEE -- The Transportation Safety Administration said Tuesday evening that terrorists may be testing security at airports across the country.

According to an intelligence bulletin dated July 20, TSA personnel have confiscated items "resembling improvised explosive device (IED) components." The items included wires, switches, pipes and "dense clay-like substances." The finds were described as a "surge in recent suspicious incidents."

The bulletin identifies Milwaukee's Mitchell International, as well as airports in San Diego, Houston and Baltimore as having the activity.

On June 4, the bulletin said, the carry-on baggage of a passenger contained "several items resembling IED components, such as a wire coil wrapped around a possible initiator, an electrical switch, batteries, three tubes, and two blocks of cheese."

The officer said the administration frequently gets reports of threats and said there is no specific credible evidence at this time.

The bulletin said previous "dry runs" preceded past terrorist attacks, including the July 2005 London subway bombings and the Sept. 11, 2001 attack on the U.S.