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.
Citing law enforcement sources, ABC News reported the couple had been "making out" in the restroom.
However, law enforcement officials told NBC News there was never more than one person occupying a single lavatory. The three passengers involved "were strangers to each other," according to a statement from the FBI, "but sat in the same row on the plane. One of the males, who was not feeling well, got up to use the restroom during the flight. The other male got up at approximately the same time to use the restroom. The female remained seated in her row. It should be noted that at no time were there ever two people in the bathroom at the same time, and at no time were the three individuals uncooperative with the flight crew."
Police detained the three passengers at Detroit's Metro Airport, but they also were eventually released.
Nearly 3,000 people were killed on Sept. 11, 2001, when hijacked commercial airliners were crashed into the World Trade Center towers in New York, the Pentagon near Washington and a field in southwestern Pennsylvania.
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 three passengers made repeated trips to the bathroom and some thought they were using hand signals to communicate, a law enforcement official said. The official was not authorized to speak publicly and spoke to The Associated Press on condition of anonymity.
Two of the men were Israeli and one was Russian, the official said, adding that the three were cleared and sent on their way.
FBI spokesman J. Peter Donald said in a statement that the jets were sent to escort the Boeing 767-200 "out of an abundance of caution." The FBI interviewed passengers and found "no nexus to terrorism," he said.
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 Airbus 318 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.
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.
Security concerns also led officials to close parts of the airport in Kansas City, Mo., on Sunday for hours and question a passenger after screeners at a checkpoint raised suspicions about the contents of a bag.
In Dallas, an FBI official says a rented moving truck parked at a curb at the Dallas-Fort Worth airport also caused a brief scare on Sunday.
FBI official Kevin Gentry says the truck was driven by a crew member of the Discovery Channel show "Sons of Guns." Investigators were suspicious because the driver said, "I got a couple of guns," but Gentry says he was just waiting for a co-worker. The two will film in El Paso and Albuquerque, N.M.
Airport spokesman David Magana says a bomb squad and canine units were deployed when an automatic weapon was found in the truck, parked in an area where troops returning from Middle East stints are greeted.
A Discovery Channel spokesman was not immediately available to comment.