Argentina has accused the US of trying to smuggle weapons and satellite phones into the country after cargo on a US military plane was seized last week.
Argentine officials say the material was not properly declared.
Argentine Foreign Minister Hector Timerman on Monday sent a formal protest to the US embassy, demanding a proper explanation about the seized cargo.
"The United States must understand that they can't send war materials without informing the government. And now they refuse to co-operate with the investigation," Mr Timerman told CNN.
The Argentine government said that the material seized at Ezeiza International Airport last Thursday included weapons, satellite communications equipment and medicine such as morphine.
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