World Bulletin / News Desk
The four -- Mohamed Houli Chemlal; Driss Oukabir, 28; Mohammed Aalla, 27; and Sahal al-Karib, 34 -- were transfered amid tight security from Catalonia to the Spanish capital.
They appeared before a judge who will decide what charges they will face in connection to last week's attacks which left 15 people dead and over 100 injured.
Prosecutors are demanding they be remanded in custody to await trail.
The men are thought to be part of a 12-strong terrorist group responsible for Thursday's vehicle attack on Las Ramblas in central Barcelona and another incident later in the Catalan town of Cambrils.
Two of the group are thought to have died in a house explosion, thought to have been caused by gas canisters they were planning to use as bombs.
Six more were shot when confronted by police, including 22-year-old Moroccan-born Younes Abouyaaqoub, the man believed to have been behind the wheel of the white van which ploughed into crowds of tourists and locals in Barcelona.