NASCAR star Kyle Busch says he was detained by authorities in Mexico last month ... after he says they found a handgun in his bag at an airport.
Busch said it all happened following the conclusion of his vacation with his wife, Samantha, in late January.
According to the 37-year-old driver, he was going through airport security screening ... when he realized he accidentally brought his firearm in his luggage.
Busch claims he has a valid concealed carry permit for it -- but its discovery still alarmed authorities, who detained him over it all.