Madrid - Spanish police arrested three suspected al Qaeda operatives Wednesday out of fear they planned an airborne attack in Europe, according to Spain's interior minister, Jorge Fernandez Diaz.

While local authorities have arrested dozens of alleged militants since 2004, when a key Madrid train station was attacked, Spanish media reported these were the first caught with explosives, meaning they had become an operational cell.

The three suspects -- two from ex-Soviet republics and a Turk -- had timers and enough explosives to blow up a bus, Diaz said in a press conference in Madrid. Police believe at least two of those arrested had practiced flying small "ultralight" airplanes or using small drones, Diaz said.

Diaz called one of those arrested a "very important member" of al Qaeda who is an expert in explosives and poison.