LOS ANGELES: A gunman with a semi-automatic weapon shot three people, killing a federal security agent, at the Los Angeles airport Friday, police said, and a suspected gunman was in custody. Flights were disrupted nationwide.

Police said the unidentified suspect, who apparently was injured following an exchange of gunfire with officers, was in custody.

Some passengers were evacuated, while others were locked down in airport restaurants and lounges. The airport was being swept for precautionary measures, and the bomb unit was on scene.

Tim Kauffman, a spokesman for the American Federation of Government Employees in Washington, confirmed that a Transportation Security Administration officer was killed.

He said the union's information came from their local officials in Los Angeles. The gunshots were reported at Terminal 3, which is home to Virgin America and other airlines.

Ronald Reagan UCLA Medical Center said it received ''three male victims from the LAX Airport shootings. One arrived in critical condition and two are listed in fair condition.''

Air traffic was affected nationwide as the Federal Aviation Administration grounded flights that had not yet departed for LAX.

Witness Brian Keech told The Associated Press he heard ''about a dozen gunshots'' from inside a security gate at the terminal.

LAX air traffic controller Michael Foote said his colleagues in the control tower saw passengers spilling from the terminal onto the tarmac, ''evacuating the building, getting out as fast as they could.''

Other travelers described a chaotic scene as airport security staff evacuated terminals, including onto to the tarmac. Hundreds of people remained gathered outside next to airplanes.

''People started saying there's a shooter, there's a shooter,'' said Natalie Morin, who was heading to San Francisco for a graduate school interview.