Agents from the US Transportation Security Administration (TSA) discovered the weapon after it triggered an alarm during screening. After opening a bag, they found a cannister with a triggering device similar to that of a hand grenade.
The grenade was labelled “smoke/yellow” and was an active weapon, according to a TSA explosives specialist and a police bomb squad, reports Fox News.
The traveller said he thought the device was not operational after buying it in an army surplus shop two years prior.
It is not clear why the man was attempting to fly with the device.
Hand grenades and realistic replicas are banned from passengers’ checked and cabin baggage in the US.
Those who break the rules can be fined up to $13,669 (£10,550) and could face criminal charges depending on the offence.
It comes after news that the number of passengers travelling through US airports with guns in their carry-on luggage tripled in July 2020 compared to the same period in 2019.
The TSA said that its officers detected 15.3 guns per million people last month, compared to 5.1 guns per million people screened during July 2019.
TSA Administrator David Pekoske said: “Even more concerning is that 80 per cent of the firearms coming into the checkpoint are loaded and it’s just an accident waiting to happen.
“Travellers need to know that if they bring a gun to the security checkpoint, regardless of whether it is in a handbag, knapsack, roller-bag or strapped to their belt, it will be an inconvenient and expensive mistake on their part.”
In the States, travellers are permitted to travel with firearms in their checked luggage, but not in their hand luggage.