A US embassy spokesman in Madrid said on Friday that Eduardo Aguirre, the US ambassador to Spain, told Spanish officials of the decision on Thursday.
Venezuela is the world's fifth-biggest oil exporter and provides subsidised heating fuel to tens of thousands of poor people in the US, but its military spending has stirred concern in Washington, increasingly at odds with Hugo Chavez, the Venezuelan president, over his self-described socialist revolution.
The aircraft are part of a $2 billion Spanish deal to supply ships and planes to Venezuela.
The spokesman confirmed a report in Friday's edition of El Pais newspaper, which said the US believed that the aircraft sale to Venezuela had the potential to complicate the situation in the South American region.
It did not elaborate on what "situation" in South America might be "complicated" by Venezuela having better aircraft.
Chavez on Friday denounced the US move.
"What is this if not evidence of the horrific imperialism of the government in Washington?" Chavez said, reading news of the US action as he began a speech to the National Assembly on the state of the nation.
Spanish state radio quoted Defence Ministry sources as saying the aircraft sale would go ahead and that the manufacturer, EADS-CASA, was in contact with French companies to provide substitute technology, although this could make the aircraft more expensive.
EADS-CASA, the Spanish division of the European aerospace giant EADS, could not be reached immediately for comment.
Spanish media reports said the US components were mostly in the engines and electronic equipment.
Zapatero said Madrid would not
bow to US policies
Jose Luis Rodriguez Zapatero, the prime minister of Spain, has defended the sale, saying Madrid would not bow to US policies.
For their part, US officials downplayed the impact of its veto of Spain's sale of military aircraft to Venezuela that contain American parts.
"US-Spanish relations are certainly much broader and deeper than one sale of military equipment," Sean McCormack, the State Department spokesman, said.
"We believe that the decision we have taken is in the policy interests of the United States government," he said.
US officials worry that the proposed sale "could contribute to
destabilisation in Latin America, and have made that view clear to the Spanish, Venezuelan and other governments in Latin America", McCormack said.
The US is also trying to block an arms deal between Brazil and Venezuela. Celso Amorim, the foreign minister of Brazil, said on Wednesday that his country saw signs that the United States was trying to block the sale of Brazilian-made military aircraft to Venezuela.
He said his country would try to persuade Washington not to interfere, Amorim said.
Chavez accused Washington on Tuesday of trying to weaken Venezuela's military power. He said he would wait to see if Brazil could solve the problem over the planes, which also include US technology.
If it could not, he suggested that Venezuela could buy similar aircraft from China.