Buenos Aires, Argentina (CNN) -- Tension between Argentina and the United States continued to simmer Tuesday as the two could not see eye-to-eye on the seizure, by Argentinian authorities, of materials that arrived on a U.S. Air Force cargo plane last week.
Argentina has accused the United States of trying to sneak weapons, drugs such as morphine, and communications equipment into their country without permission. The United States says that if there was a problem with the items, it should be resolved privately between the two parties.
The spat revolves around the arrival of a U.S. cargo plane in Argentina. Its mission was to provide materials for a joint training course with Argentinian federal police on hostage rescues. Argentinian Foreign Minister Hector Timerman said the Americans did not properly declare about a third of the items that were aboard the plane, violating local laws.
The material had not been included on a list from the U.S. government that the Argentinian government approved.
Such material cannot enter the country without proper authorization, Timerman told CNN en Español.
"Argentina has suffered two terrorist attacks, and we have very strict laws about what can enter and what cannot enter the country, to prevent a third incident," he said.
The items that were not declared included wiretapping equipment, communications equipment and what Timerman described as "secret things."
American troops on the cargo plane at first blocked Argentinian agents from examining some of the undeclared cargo.
"When finally, after six hours of talk, we convinced the American soldiers to open this famous green suitcase, they pleaded with us not to open it outdoors, but in a closed space, because if it were photographed by spy satellites, U.S. security would be at risk," Timerman said.
He added, with emphasis, "What were they bringing? That's what the Argentinians want to know."
U.S. Assistant Secretary for Western Hemisphere Affairs Arturo Valenzuela denied that the United States had not declared certain items, and said that everything on the cargo plane was for use during the hostage-rescue course.
"We're surprised by Argentina's reaction to this issue," Valenzuela told CNN en Español.
His view is that if there was any problem, it could have been handled privately, "with respect," and not in the public sphere.
"There was no intent here to violate Argentine laws," he said.
The United States also wants its cargo back.
"It's absolutely necessary that those materials be returned immediately," Valenzuela said.
Timerman said the items would be returned only after investigators are done examining them.