Sen. Rand Paul of Kentucky, the son of Republican presidential candidate Ron Paul and a frequent critic of the Transportation Security Administration, was stopped by security at the Nashville airport Monday when a scanner set off an alarm and Paul declined to allow a security officer to subsequently pat him down. The White House said airport security acted appropriately.

Police escorted Paul away, but he was allowed to board a later flight. The security scanner identified an issue with the senator's knee, although Paul said he has no screws or medical hardware around the joint.

Paul, who frequently uses the airport about an hour from his home in Bowling Green, Ky., told The Associated Press in a telephone interview that he asked for another scan but refused to submit to a pat down by airport security.

Paul said he was "detained" at a small cubicle and couldn't make his flight to Washington for a Senate vote scheduled later in the day.

White House spokesman Jay Carney did not confirm that the incident involved Paul, but said the passenger in question was never detained. He defended the TSA.

"Passengers, as in this case, who refuse to comply with security procedures, are denied access to the secure gate area," Carney said. "I think it is absolutely essential that we take necessary actions to ensure that air travel is safe and I believe that is what TSA is tasked with doing."

Paul said the situation reflects his long-standing concern that the TSA shouldn't be "spending so much time with people who wouldn't attack us."

TSA spokesman Greg Soule confirmed there was an incident but didn't identify the passenger as Paul.

"When an irregularity is found during the TSA screening process, it must be resolved prior to allowing a passenger to proceed to the secure area of the airport," Soule said in a written statement. "Passengers who refuse to complete the screening process cannot be granted access to the secure area in order to ensure the safety of others traveling."

Carney said an alarm was triggered during routine screening, but the passenger refused to continue with the screening process to resolve the issue. Local police escorted Paul out of the screening area, he said.

Paul went through a millimeter wave machine that uses a generic outline of a body for all passengers, according to a TSA official who spoke on condition of anonymity to discuss agency screening procedures. When an alarm goes off, TSA officers target the area of the body that triggered the alarm and pat down the passenger.

Paul's father, Ron Paul, used his son's experience to promote his "Plan to Restore America," which would cut $1 trillion of federal spending in a year and eliminate the TSA.

"The police state in this country is growing out of control. One of the ultimate embodiments of this is the TSA that gropes and grabs our children, our seniors, and our loved ones and neighbors with disabilities," Ron Paul said in a statement issued by his presidential campaign. "The TSA does all of this while doing nothing to keep us safe."

Rand Paul told reporters at the airport that he had no idea why his knee raised concerns with TSA. He said he showed his knee to the security agents and doesn't have any medical hardware or issues in the knee.

"There is no problem. It was just a problem with their machine. But this is getting more frequent, and because everybody has to have a pat down it's a problem," Paul said.

Paul said he was in Denver two days ago and allowed to walk through the screener again and avoided the pat down.

He said he didn't want special treatment from TSA because he's a senator. "I think we need to treat everybody with dignity."

The TSA said Paul was allowed to board another flight after a different screening.

In a November Senate hearing, Paul asked TSA Administrator John Pistole to change the policy so that adults could go through the machines a second time when an alarm is triggered on the first attempt.

"Let us go back through the machine rather than get a pat-down. You'll get rid of a lot of the anger and animosity towards the TSA and towards what you're doing, and give us a little more dignity when we travel," Paul said. "Just let us go back through the screener again _ you know, I mean, people don't want to have a pat-down."

Paul is a member of the Senate Homeland Security and Governmental Affairs Committee. The committee does not regulate TSA, but holds hearings about airport security.

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Schelzig contributed to this story from Nashville. Writer Roger Alford contributed from Frankfort, Ky.