A North Carolina student has admitted placing box cutters and other suspicious items on two Southwest Airlines planes, officials say.
Thousands of planes are being checked
The admission reportedly came during questioning of the 20-year-old man by US federal investigators in Baltimore, Maryland.
Security checks were ordered for every commercial airliner in the US after the items were discovered.
The student had informed the Transportation Security
Administration (TSA) that he planned to put packages on planes in
an effort to expose gaps in aviation security, a congressional official told the Associated Press.
"It doesn't appear to be a terrorist event. I think it is safe to
fly," FBI Director Robert Mueller said.
Law enforcement sources say the man - described as a male student of Guildford College in Greensboro, North Carolina - was a passenger aboard the planes and not an employee of the airline or airports.
They said he was co-operating with officials and so far had not been charged.
The TSA said the man was tracked down, partly as a result of an e-mail sent to the agency in which he cited items "linked" to the discovery.
Restrictions on carry-on items were tightened after 11 September 2001
The TSA said the man had been under investigation for "several months".
The items found aboard the two planes - one in New Orleans, the other in Houston - included box cutters, clay that resembled plastic explosives and bleach, sources familiar with the investigation said.
The liquid was contained in suntan lotion bottles; the clay was inside Play-Doh containers.
Box cutters were used by attackers who hijacked four planes on 11 September, 2001, and crashed them deliberately in New York and Washington killing more than 3,000 people.
Southwest Airlines said notes found with both packages said the intention was to simulate a threat and to challenge the security screening procedures for passenger planes.
The company said its employees found the potential weapons on Thursday evening. It said subsequent inspections of its entire fleet of 385 aircraft had found no further suspicious items.