A record number of firearms were discovered at U.S. airport security checkpoints last year, 87% of which were loaded, the Transportation Security Administration (TSA) said Wednesday.

TSA found 4,432 firearms in 2019, a 5% increase compared to the previous year, and the highest recovered in the agency’s 18-year history, according to a statement.

The firearms were found in carry-on luggage and on passengers at 278 airports across the country.

With 323 cases, the Hartsfield-Jackson Atlanta International Airport had the most firearms discoveries, followed by Dallas-Fort Worth International Airport, Denver International Airport and George Bush Intercontinental Airport in Houston, which all ended the year with more than 130 cases.

The TSA said it also found a slew of explosives and sharp objects throughout the year, some of which passengers had tried to conceal in items like boots.

“Please don’t pack your firearm in your carry-on bag and please check your bags before heading to the airport,” the TSA urged in its blog post, cautioning of penalties of more than $13,000 per violation and potential arrest.

Passengers are permitted to transport unloaded firearms in locked hard-sided luggage as checked baggage.

The record-breaking number of attempts to carry on firearms may be in part attributable to passenger numbers. The TSA said that 2019 featured the busiest spring break travel period and Fourth of July holiday weekend on record. But the busiest day on record was Dec. 1, when more than 2.8 million passengers and crew members were screened.

In January, a passenger was able to board a Delta Airlines flight from Atlanta to Tokyo with a gun. The passenger reported the firearm to the airline and was “met by Japanese authorities upon landing.” The TSA said that it would “hold those responsible appropriately accountable.”

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Write to Amy Gunia at amy.gunia@time.com.