An American Airlines flight bound for New York City was halted just before takeoff Thursday after someone called in a threat against the jetliner that was later described by the FBI as non-credible.

Still, the threat rattled nerves in San Francisco and beyond and marked the latest in a series of airline scares in the past year.

A witness said two passengers in the back row attracted suspicion after the threat was reported and were taken off the plane in handcuffs. But a law enforcement official later said no one was in custody.

American Airlines Flight 24 had been scheduled to take off at 7:30 a.m. Thursday at San Francisco International Airport and was grounded around 10 a.m. after a late departure from the gate. Passengers were removed from the plane and taken by buses to a terminal where they were sent through security again.

It was not clear if it was a bomb or hijacking threat, but a second federal law enforcement official who received an investigative update on the case says it was not a credible one.

The official says the FBI in San Francisco recorded the threat as a potential hijacking. The threat was relayed more broadly throughout the FBI as a potential bombing. The two officials spoke on condition of anonymity because the investigation was ongoing.

The incident occurred on a Boeing 767 that had already been delayed for at least two hours with 163 passengers and a crew of 11. It finally pulled away from the gate at 10 a.m., only to taxi to a remote section of the tarmac where passengers sat for another two hours.

"There was no fear in the cabin at all," passenger Michael Kidd told The Associated Press in an interview. "It was pretty calm. Even with the frustration of having to sit there, there were no raised voices."

Passengers with Internet access searched the Web for details about the incident. Flight attendants admonished passengers who tried to get up and reach their overhead luggage, Kidd said. Passengers were allowed to go to the bathroom one at a time, he said.

Police eventually entered through the back door and arrested the two passengers. Others on board were taken off the plane six at a time and put on a buses. San Francisco Police Department officers screened them and their carry-on luggage with hand-held security wands.

The threat report originated from clerk at a business in Alameda, a city across San Francisco Bay from the airport, said Lt. Bill Scott. The clerk called dispatchers at Alameda Police Department shortly after 9 a.m. Thursday and said her business had received an anonymous phone call "making a threat specifically about Flight 24," Scott said.

"All passengers are safe and out of an abundance of caution, TSA requested the plane be moved to a remote location," TSA spokeswoman Suzanne Trevino said in a statement.

It was the latest in a line of airplane scares in the past year, including the attempted Christmas bombing of a Detroit-bound jetliner by a Nigerian. In April, a Qatari diplomat who was on his way to an official visit with an imprisoned al-Qaida sleeper touched off a bomb scare in Colorado by slipping into an airline bathroom for a smoke.

One of the four hijacked flights on Sept. 11, 2001, was bound for San Francisco. United Air Lines Flight 93 left Newark International Airport for San Francisco and crashed into a field in Pennsylvania.

Passenger Randy Cohen, 50, of New York said he lived across street from the World Trade Center on Sept. 11.

Cohen said the atmosphere on the plane was generally calm even though passengers got little explanation about why the plane had been diverted. But he said rumors about a hijacking or bomb threat began floating around among passengers connected to the Internet. "It was like, man, this can't happen again," Cohen said.

At the same time, via its Twitter feed, American Airlines reassured a passenger sending out tweets from aboard the aircraft.

"Hang in there," the airline said, "the authorities are taking care of things."