Still, officials said they did not believe the bags were placed there as a prelude to a terrorist attack.

"It doesn’t appear to be a terrorist event," FBI Director Robert Mueller said during a visit to the FBI field office in Houston. "I think it is safe to fly."

Homeland Security Department spokesman Brian Roehrkasse described the searches as "a precautionary measure." They were expected to be completed within a day.

Air carriers in Hawai'i were complying today with the order. The carriers will be doing their own searches, said Sidney Hayakawa, federal security director for the Transportation Security Administration at Honolulu International Airport.

Hawaiian Airlines spokesman Keoni Wagner said today Hawaiian had received the TSA directive and the search should not affect the airline’s flight schedule. Aloha similarly said it was complying with the request.

Southwest employees doing routine maintenance found the items in small plastic bags left in the lavatories of planes in New Orleans and Houston last night, according to a statement from the airline. The items were turned over to government officials and the FBI and Transportation Security Administration immediately began investigating.

The statement said the items appeared "intended to simulate a threat" and that each bag was accompanied by a note that "indicated the items were intended to challenge Transportation Security Administration checkpoint security procedures."

"We will not speculate on who might have left these items on board," the statement said.

Southwest said security checks of its entire fleet of 285 aircraft found no other suspicious items.

The New Orleans flight had originated in Orlando, Fla., and was scheduled to go on to San Diego last night, said Southwest spokeswoman Beth Harbin. The crew reported a lavatory wasn’t working and a maintenance worker discovered the bag at about 9 p.m., she said. The other aircraft was in Houston for routine maintenance when the bag was discovered a short time later.

In addition to the box cutters and notes, the bags contained bleach and some form of clay, according to a senior law enforcement official speaking on condition of anonymity. Clay can be used to hide explosives or attach them to other surfaces, while bleach could be thrown in a person’s eyes to temporarily blind them.

The 19 al-Qaida operatives who hijacked planes and crashed them on Sept. 11, 2001, used box cutters as weapons. After the attacks, box cutters were added to the list of items banned from carryon bags.

Government officials played down the possibility of a terrorist connection, though FBI spokeswoman Susan Whitson said members of the bureau’s joint terrorism task forces are involved in the investigation.

Harbin said Southwest does not believe the items found were connected to a plot to hijack the airplanes.

Al-Qaida and its affiliated terrorist groups have long had an interest in using aircraft as weapons. The FBI and Homeland Security Department have issued numerous warnings about possible tactics terrorists could use, including use of small carryon items such as cameras to blow up airplanes.

The Associated Press and Advertiser staff writer Rod Ohira contributed to this report.

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TSA: www.tsa.gov