The authorities in Venezuela have accused the US embassy in Caracas of importing cargo illegally after halting lorries carrying diplomatic baggage.
Venezuela says 16 out of 20 packages broke the rules
Cargo found arriving at Caracas airport included parts for military aircraft ejector seats and chicken meat, said Interior Minister Jesse Chacon.
"Everything that doesn't pass through customs is contraband, we are talking about contraband here," he said.
Denying wrongdoing, the US demanded to know why diplomatic cargo was searched.
"The impounded cargo consisted of household effects of a US diplomat and a shipment of commissary goods," said US state department spokesman Edgar Vasquez.
The search, he added, had violated long-established procedures.
"We have requested an immediate explanation of the entire incident," he said.
Relations between Washington and Caracas have long been strained with Venezuela accusing the Americans of not respecting its sovereignty and the US viewing the leftist government of President Hugo Chavez with growing suspicion.
Displaying a photo of the lorries for journalists, Mr Chacon said that only four out of 20 packages were considered diplomatic baggage covered by international protocol.
The US had bypassed customs and the necessary paperwork with the other 16 which included 80 kilos (176 pounds) of chicken, he said.
"They brought in food goods without any health controls, they brought in armaments without any legal control," he told reporters.
"It's not the Venezuelan government that is making violations - it's the US embassy that's making them."
Washington officials said that the cargo, which was delivered by a US military plane, included replacement ejection seat parts for Venezuelan combat planes but no weapons or arms.
Mr Chacon said the Venezuelan air force had requested ejection seat propulsion motors but the cargo contained items it had not asked for such as cartridge devices, detonator fuses, rocket motors and pliers.