The Spanish prime minister has defended a plan to sell arms to Venezuela amid US concern that the deal could destabilise countries in Latin America.
Mr Zapatero said the plan would help Venezuelan border security
Jose Luis Rodriguez Zapatero is expected to finalise the purchase of ships and planes worth 1.3bn euros ($1.7bn) in Venezuela on Wednesday.
He said the military equipment was designed to help regional security and to counter drug trafficking.
The proposed deal has been denounced by Mr Zapatero's political foes in Spain.
Spain's conservative opposition leader Mariano Rajoy described the plans as a "monstrous error" and said Venezuelan opponents of President Hugo Chavez had also criticised the proposal.
The row in Spain follows international concern over Venezuelan plans to buy 100,000 AK-47 assault rifles from Russia.
The US state department has accused Venezuela of starting an arms race and has suggested the rifles could end up in the hands of Colombia's left-wing Farc rebels.
But Venezuela and Russia have both dismissed the US objections, saying the deal does not break international law.
Mr Zapatero said the proposed agreement for the Venezuelan military to purchase surveillance aircraft and patrol boats should not cause concern.
"It represents a stance in defence of security," he said in comments broadcast on Spanish radio.
In talks on Wednesday, Mr Zapatero told Mr Chavez's opponents he would take into account their concerns about the deal and the Venezuelan leader's record on civil liberties.
On Tuesday, the Spanish prime minister attended a summit with Mr Chavez and the presidents of Colombia and Brazil.
Spain was the region's pre-eminent ally, he said at the end of the talks.