New York ? Fighter jets escorted two flights — one to New York City, another to Detroit — after passengers’ use of the bathrooms aroused suspicions Sunday, the 10th anniversary of the Sept. 11 attacks.

On a Los Angeles-to-New York American Airlines flight, three passengers made repeated trips to the bathroom, officials said. The three were cleared after the plane landed safely 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 after the plane landed without incident. They were released after questioning.

In both instances, the FBI said the jets shadowed the planes “out of an abundance of caution.”

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, the crew used “normal procedures” to assess the circumstances and the plane landed as planned, Smith said.

“In our eyes, it’s a big nothing,” Smith added.

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