NEW YORK (AP) -- Fighter jets were scrambled to escort two commercial flights into New York City and Detroit "out of an abundance of caution" after crews reported suspicious activity on the 10th anniversary of the Sept. 11 terrorist attacks, officials said.

The bathroom use by some passengers aroused the suspicion Sunday, but all were released after being questioned by authorities on the ground.

On an American Airlines flight from Los Angeles, three passengers who made repeated trips to the bathroom were cleared after the plane safely landed at New York's Kennedy Airport.

Earlier, on a Denver-to-Detroit Frontier Airlines flight, the crew reported that two people were spending "an extraordinarily long time" in a bathroom, Frontier spokesman Peter Kowalchuck said. Police detained three passengers at Detroit's Metropolitan Airport, but they also were eventually released.

In a statement Monday, the FBI said there never were two people in the bathroom at the same time.

Asked late Sunday if authorities may have overreacted, airport spokesman Scott Wintner said the airport's response wasn't unusual and the same steps would have been taken any other day of the year.

"Regardless of why it was triggered, whenever we get a radio call of a security problem on board, our response is the same one we would have had yesterday, tomorrow," Wintner said.

"We always react as if it's the end of the world," he added. "If it isn't, so be it."

New York, in particular, has been in a heightened state of security after federal officials received a credible but uncorroborated tip of a car bomb plot on the 9/11 anniversary in either New York or Washington.

American Airlines spokesman Tim Smith said the plane's captain never declared a security threat and never asked for law enforcement help. A "security concern" was brought to the airline's attention and the crew used "normal procedures" to assess the circumstances, he said. The plane landed as planned.

"In our eyes, it's a big nothing," Smith added.

Still, the North American Aerospace Defense Command scrambled two F-16 fighter jets to shadow American Airlines Flight 34 until it landed safely at 4:10 p.m., the Transportation Security Administration said in a statement.

On the flight, the men made several trips to the bathroom, and appeared to be giving each other hand signals that were misinterpreted by crew members and at least one passenger, the FBI said. Federal officials determined it was innocent behavior.

Two of the men were Israeli and one was Russian, according to a law enforcement official, adding the three were cleared and sent on their way. The official was not authorized to speak publicly and spoke to The Associated Press on condition of anonymity.

The jets were sent to escort the flight "out of an abundance of caution." The FBI interviewed passengers and found "no nexus to terrorism," FBI spokesman J. Peter Donald said in a statement.

A similar scenario played out on Frontier Flight 623.

NORAD spokesman John Cornelio said the agency sent two F-16 jets to shadow the plane until it landed safely. The craft, with 116 passengers on board, landed without incident at 3:30 p.m. EDT and taxied to a pad away from the terminal, he said. The plane was searched, and authorities cleared the aircraft at 5:15 p.m. EDT, according to the TSA.

The flight originated in San Diego before stopping at Denver International Airport on its way to Detroit. The FBI said the jets shadowed the Detroit-bound plane for the same reason as in New York - "out of an abundance of caution" - and nothing was found during the search.

The three escorted off the Frontier flight in handcuffs included two men and a woman, passenger Ilona Hajdar of Charlotte, Mich., told The Associated Press.

The FBI said the three didn't know each other. One man felt ill and got up to use the restroom and another man in the same row also left his seat to go to the bathroom. The FBI said they never were inside together.

"At no time were the three individuals uncooperative with the flight crew," the FBI said.

Hajdar, 27, said she'd been asleep for most of the flight but realized there was a problem when the plane's bridge didn't extend at the gate. The plane then rolled to a remote spot on the airfield. After about a half hour, police SWAT boarded.

Fellow passenger Belinda Duggan of Troy, Mich., said the plane taxied by the gate and headed for a remote patch of tarmac.

"All of a sudden, a SWAT team went through and saying, `Please place your hands on the seat in front of you,'" Duggan said, adding that police had three dogs with them.

American Airlines passenger Steven Ciobo said nothing seemed amiss on the flight to New York until he saw police lights on the runway after the plane landed. He said airline workers told passengers to remain seated and that the authorities would meet the plane, and everyone was quiet as air marshals got on board and headed for the back.

"To be honest, I think it's reassuring that there was such a great response from the authorities," Ciobo said. "If there are people that are stupid enough to do those things on today of all days you wonder what's going on through their heads. But the fact that there were so many authorities there ... and that it all went so smoothly, I think they did a good job."

The jets intercepted the flight about 100 miles west of New York and shadowed it until it landed, Cornelio said.

American Airlines is a subsidiary of AMR Corp. Frontier is a subsidiary of Republic Airways Holdings Inc.

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Goodman reported from Detroit. Associated Press writers Colleen Long and David B. Caruso and AP Television Reporter Bonny Ghosh in New York, Jeff Karoub in Detroit and P. Solomon Banda and James Anderson in Denver contributed to this report.

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