Two people had been arrested in Barcelona and Igualada, 60 kilometres (40 miles) west of the Catalan capital, as part of the raid, the spokesman for Catalonia's police force, the Mossos d'Esquadra, told AFP. Further arrests were expected, he added.
“The goal (of the cell) was to attack but we are still investigating which places may have been targeted,” the spokesman said.
Over 100 officers were taking part in the “counter-terrorism operation” launched by the Catalan police force at six am (0500 GMT), the Mossos said on Twitter.
POLICE COUNTER-TERRORISM OPERATION in process. We are doing 6 entrances in Barcelona and Igualada as a result of a long investigation ordered by Audiencia Nacional
— Mossos (@mossos) January 15, 2019
Police stormed five properties in Barcelona and a sixth in Igualada as part of the operation.
Armed officers, wearing black ski masks, stood guard outside a building in central Barcelona as boxes and bags were removed from a flat, according to an AFP reporter on the scene.
The operation was ordered by Spain's High Court, which is charged with terrorism investigations, and it is focused on “the crimes of terrorism, public health offences and organised crime”, the Mossos said.
Barcelona was on alert last month after the US State Department warned off the risk of a terrorist attack in Spain's second-largest city over Christmas.
On August 17, 2017, a van rammed crowds on Barcelona's Las Ramblas boulevard, killing 14 people and injuring over 130 others.
The 22-year-old Moroccan driver then stole a car after killing the driver and fled.
Several hours later five of his accomplices mowed down pedestrians on the promenade of the seaside resort of Cambrils, south of Barcelona, before stabbing a woman to death.
The Islamic State group claimed responsibility for the attack, Spain's deadliest in over a decade.