A passenger who caused an evacuation at Kennedy International Airport has told law enforcers that he breached security after going outside to smoke and then misplacing his boarding pass.

William Contreras Ramos, 20, of San Lorenzo, Puerto Rico, was being detained upstate today until the FBI could come get him, according to Albany County Sheriff James Campbell.

Mr. Ramos told sheriff’s deputies that he had noticed he was running late and didn’t have his boarding pass, so he went through another door and was able to get to his flight’s gate.

He had no weapons on him, but a straight razor was found in his carry-on luggage, Sheriff Campbell said.

Thousands of passengers and dozens of flights were delayed for several hours during the evacuation and subsequent security rescreening.

The passenger walked up an exit lane past a private security guard at terminal two at about 6:40 p.m. yesterday, the TSA said.

The guard could not immediately locate the passenger and notified the TSA of the security breach, sparking a wide search for the man at terminals two and three, the federal agency said.

“He was going through the exit lane. That’s going the wrong way,” a TSA spokesman, Norm Brewer, said. “As I understand it, he was challenged and stopped. And then what happened, I do not know. He at some point ended up beyond that exit approach and the rest is sort of history.”

The Port Authority, which runs the airport, called the sheriff around 6:45 p.m. to say the man had boarded a plane to Albany. Deputies there boarded the plane and took him in for questioning.

The TSA said in a statement on its Web site that “there is no known nexus to terrorism at this time.”