He said police yesterday arrested two men from former-Soviet republics close to Ciudad Real who were likely heading to France, and a Turkish man near Cadiz whose house was searched and where explosives were found.
The minister said one of the two arrested near Ciudad Real was a senior al-Qaeda operative who had extensive experience in bomb-making.
"It is one of the most important operations against al-Qaeda to date to be carried out on an international level," he said.
"There are clear indications that the suspects arrested could have been planning an attack in Spain, and or, other European countries," the minister told a news conference.
He said the operation was conducted with the help of other international police forces, and that the explosive material was being analysed. No details were given on how much material was found, though the minister said it was enough to blow up a bus.
An attack in 2004 outside a key railway station in Madrid which killed 191 people was blamed on al-Qaeda.