Ports and ships are operating under heightened security after the Coast Guard warned of a possible terrorist attack by either swimmers or divers.

Cmdr. Jim McPherson, a spokesman for the Coast Guard, said Monday the warning was issued over the weekend after the agency received reports of a possible attack. The Bush administration warned last month of possible terrorist activity by scuba divers.

The new warning went to local Coast Guard units, who then notified port authorities, marine patrols and the maritime industry, he said, and added that the Coast Guard offered specific actions that ports could do to increase security.

McPherson would not elaborate on the nature of the warning nor the security measures.

Homeland Security chief Tom Ridge said during the weekend that Al Qaeda was interested in training terrorists to attack ports and ships.

McPherson asked anyone noticing suspicious maritime activity should call the Coast Guard at 1-800-424-8802.

In a related matter, McPherson said the Coast Guard planned to transport bomb-sniffing dogs by helicopter to ships at sea, lower them and their handlers by cable to the ship, and have them look for explosives. This will be part of the agency's new maritime security team to be formed this summer. In addition, inspectors now trained to look for hazardous materials will be asked to also check for explosives or chemical weapons, McPherson said.