Three suspected members of the al-Qaida terror group are being questioned in a Spanish court, where a judge will decide whether they remain behind bars.
Armed police shut down streets in Madrid Friday as the three men were led into the Audiencia Nacional Court.
Spanish officials say the suspects are of Russian and Turkish origin, and that the Turkish suspect had enough explosives to blow up a bus.
The two suspects of Russian origin were arrested earlier this week as they were making their way toward the French border. Officials arrested the Turk in the southern part of the country.
Spanish media reported the suspects had been experimenting with ultra-light aircraft as a possible delivery mechanism for a bomb.
Some information for this report was provided by AP and Reuters.