Coast Guard Lt. Cmdr. Todd Offutt confirmed that the Coast Guard was investigating "suspicious activity ... observed by CG personnel" but declined further comment.

But a source, who requested anonymity because of the continuing investigation, said the "suspicious activity" involved a scuba diver who was seen near the station at 12:30 a.m. The Coast Guard requested assistance from the Joint Terrorism Task Force and newly created State Law Enforcement Coalition to conduct a land and water investigation.

Honolulu Harbor remained open but the Coast Guard was using divers and several boats for the investigation.

Federal and state officials were also questioning boaters at Kewalo Basin and Ke'ehi Small Boat Harbor.

Brian Benton, owner of Kewalo-based Dive Oahu, said a U.S. Customs agent questioned him today. "He asked if we rented or filled any black tanks," Benton said.