Los Angeles (CNN) -- Authorities intensified their investigation Tuesday into a mystery at Los Angeles International Airport: Who's behind the explosions of dry ice in containers for two days in a row?
For the moment, police say they don't believe terrorism is at work. No injuries have been reported in the explosions.
"This appears to be an internal job, maybe a labor dispute or a prank," said Los Angeles Police Deputy Chief Michael Downing. "But we do take this very seriously. This is along the lines of planting a pipe bomb.
"It's a destructive device. The detonation or possession of a destructive device is a felony," Downing added.
The incidents demonstrated that LAX has vulnerabilities, Downing said. The airport is the sixth busiest in the world and third busiest in the United States, according to its website.
"I think it does reveal a vulnerability that we're gonna shore up and that is that you have cameras in public access areas," Downing said. "We should also have cameras in restricted access areas to maintain the integrity of the security system."
Los Angeles police Detective Gus Villanueva said there's "no nexus to terrorism at this point."
The FBI has been called in, though Los Angeles police are the lead investigating agency, said FBI spokeswoman Laura Eimiller.
"There's no established motive based on the evidence, and there is no articulated threat associated with the various incidents. Until a suspect or suspects are identified, it would be difficult to comment on motive," Eimiller said.
When asked if the explosions were a prank, she said: "There are many reasonable theories in a situation like this, and none have been ruled out."
Dry ice, which is carbon dioxide in solid form, is used as a refrigerant for meats and ice cream, especially when shipped in a box. When dry ice becomes warm, it transforms into vapor.
The more recent incident occurred at 8:30 p.m. Monday at the Tom Bradley International Terminal, airport police said.
CNN affiliate KCAL said the blast took place in an employee restroom, inaccessible to nonemployees.
Three plastic bottles containing dry ice were found, but only one had exploded, Villanueva said.
Police and bomb experts cleared the scene by about 9:45 p.m., KCAL reported. There were no injuries, and no flights were delayed.
On Sunday, dry ice in a plastic bottle exploded in an employee restroom at the airport, causing a brief shutdown of Terminal 2, the FBI said. No injuries were reported, and Terminal 2 resumed operations after a brief evacuation.
The airport has nine terminals.
CNN's Paul Vercammen contributed to this report.