Three airline passengers questioned after their "suspicious activity" prompted a military fighter jet escort into Detroit airport on the anniversary of the September 11 attacks have been released without charges, the FBI said on Monday.
Frontier Airlines flight 623 from Denver to Detroit was one of two US commercial airliners escorted by fighter jets on Sunday's 10th anniversary of the attacks on the World Trade Centre and the Pentagon.
FBI Special Agent Sandra Berchtold said the plane was diverted as a precaution "based on reports of suspicious activity on the plane during flight and the heightened security measures during the 10th anniversary of September 11."
The three passengers, two men and a woman, were questioned along with crew members and several other passengers and no threat was found, Berchtold said.
The three passengers were sitting in the same row of the plane, but did not know each other, Berchtold said. One of the men got up to use the bathroom during the flight because he was not feeling well and the other man did the same, she said.
Berchtold said the FBI wanted to dispel media reports that there had been sexual activity on the plane.
"At no time were any two people in the bathroom at the same time, and the three individuals who were questioned were totally cooperative with us... and they were never uncooperative with the flight crew," Berchtold said.
In the second incident, two US F-16 fighter jets escorted the transcontinental American Airlines flight 34 to its destination, John F. Kennedy Airport, on Sunday after reports of suspicious activity by three passengers.
Passengers on the Boeing 767 flight from Los Angeles disembarked without incident, the airline said.
US authorities were on high alert during the anniversary because officials said they had received "credible but unconfirmed" information last week of possible attacks being planned around the date.