At least three people, including an unidentified gunman, have been shot dead at Los Angeles International Airport, American officials have said.

News of the shooting - which also left several wounded - came as US cities were on high alert for possible attacks as Americans celebrate Independence Day.

Los Angeles Mayor James Hahn

We have no information that indicates that this incident is connected to any terrorist

The airport shooting took place near the ticket office of the Israeli airline El Al, at the Tom Bradley International Terminal.

FBI officials said there was no indication that it was a terrorist attack, but added it was too early to rule anything out.

Earlier, the Israeli Transport Minister Ephraim Sneh had said he thought the shooting was a terrorist attack.

"When a gunman opens fire on El Al passengers at an international airport, you have to assume it is terrorism," Mr Sneh said.

But Los Angeles Mayor James Hahn said authorities had no indication so far that the shooting was "connected to terrorism".

Reports in the US media are suggesting the gunman may have borne a grudge which may have motivated his action.

Flurry of fire

A security official employed by the airline returned fire and the gunman was killed.

The guard is reported to have suffered stab wounds.

The police have said they have two people in custody whom they are now questioning.

The airport terminal had been closed as ambulances and police cars arrived at the scene to take away victims, but is now returning to normal.

Today was supposed to be a pretty secure day

Witness Thad Weimlein

A witness, Thad Weimlein, described an initial flurry of fire, followed by silence then more gunfire.

He told KCBS TV news channel he saw plainclothes policemen pulling out their guns and badges at the same time.

At first, "a lot of people thought it was fireworks and a prank," he said.

"There were probably eight to 10 shots, people were running and screaming, hitting the floor," he said.

"Today was supposed to be a pretty secure day," he said.

Busy travel day

The BBC's David Willis who is at the airport said many people there were in tears after the shooting.

The airport was very busy as people prepared to travel across the US on Independence Day, he said.

Explosives experts have been brought in, as well as policemen with sniffer dogs to check for possible further suspects, he said.

The White House Office of Homeland Security is monitoring more than 2,000 celebratory events throughout the country.

Military jets are patrolling the skies above key cities while thousands of extra police, troops and FBI agents have been deployed across the country.

Plane crash

In a separate incident, a small plane has crashed into a crowd of people near a theme park east of Los Angeles, killing one person and critically injuring six people, officials said.

The victim is said to be the pilot, who had reported he was having mechanical problems.

The crash in San Dimas, California, about 50 kilometres (35 miles) east of Los Angeles, happened at about midday (1900 GMT), a Los Angeles Fire Department official said.