The U.S. Department of Transportation and the FBI warned this month that future Al-Qaeda targets may have high symbolic value and cause mass casualties, severe economic damage and maximum psychological trauma.

However, FBI analysts also said terrorist sleeper cells already in the United States might seek "softer" targets that would be attacked by truck bombs, commercial or private aircraft, small watercraft or explosives that are easily concealed.

The warning comes after firearms attacks against U.S. Marines in Kuwait, the fatal shooting of a U.S. diplomat in Jordan, the bombing of a nightclub district in Bali, the attempted sinking of a French oil tanker and the taking of hostages by Chechen guerrillas at a Moscow theater.

Even though recent terrorist activity has occurred overseas, the U.S. government is urging citizens to remain vigilant about possible attacks on U.S. soil. The DOT is asking the transportation industry to report information concerning suspicious activity to their local FBI office through the FBI Web site at http://www.fbi.gov/contact/fo/fo.htm or to the National Infrastructure Protection Center at http://www.nipc.gov/incident/cirr.htm.

Truckers who observe suspicious activity involving the nation's water, power or transportation systems can report it to the NIPC's toll-free number, 1-888-585-9078. The NIPC also has a general "tips" phone that connects directly to the FBI. The phone number is (202) 323-3104.