The agency said that it found 4,432 firearms last year in carry-on bags or carried by passengers, neither of which is allowed. That number was 5% higher than the 4,239 firearms discovered in 2018 and nearly five times the 926 found in 2008, the TSA said.

A vast majority of the guns found in 2019 — almost 90% — were loaded, the TSA said. About one-third of the guns caught had a round in the chamber.

“The continued increase in the number of firearms that travelers bring to airport checkpoints is deeply troubling,” David Pekoske, administrator of the TSA, said in a statement Wednesday. He advised flyers to follow the rules of the “proper way to travel safely with a firearm.”

The airports where the most firearms were found in 2019 were at three major hubs: 323 at Hartsfield-Jackson Atlanta International, 217 at Dallas/Fort Worth International and 140 at Denver International.

The TSA did not offer a possible explanation for the uptick and did not respond to a request for comment Wednesday. In many cases, experts said, passengers forget the firearms are even in their luggage.

Travelers are allowed to transport firearms in their checked baggage if they are “unloaded, packed in a locked hard-sided case,” the TSA said in its statement. Passengers should then bring the case to the check-in counter and tell an airline representative that they want to travel with a gun.

The agency has for years warned against not following those rules, often using some of the extreme items found in passengers’ luggage to remind the public about airport security rules.

The TSA found a missile launcher in a man’s checked luggage at Baltimore-Washington International Airport in July, for instance. He had told authorities that he was an active member of the military and wanted take the missile launcher home with him to Jacksonville, Texas, as a souvenir from Kuwait. The weapon was confiscated.

Not all firearms are caught. In January 2019, a Delta Air Lines passenger carried, by accident, a loaded gun through a security checkpoint at Atlanta’s international airport. The passenger later discovered the firearm and alerted authorities, who met the plane when it landed in Japan.

In 2017, a shooting at an airport in Fort Lauderdale, Florida, highlighted the issue of guns at airports after a gunman retrieved a weapon from his checked bag, opened fire and killed five people.

Federal rules allowing guns to be checked at airports have sometimes caused confusion among passengers traveling to cities with strict firearm regulations. Some visitors to New York City, for example, have been arrested upon checking guns for return flights home, unaware that they cannot legally possess guns in the city without a city gun permit.

This article originally appeared in The New York Times .