Police said on Sunday they have found more than 120 gas canisters in a house in Alcanar, where suspects of this week’s twin assaults in Spain were believed to be building bombs for “one or more” attacks in Barcelona.

“We’re starting to see clearly that [the Alcanar house] was the place where they were preparing explosives for one or more attacks in the city of Barcelona,” police chief of Catalonia region Josep Lluis Trapero told journalists.

On the eve of the attack in Barcelona, an explosion had occurred at the house about 200 km south of the city, and police believe it was detonated in error by the suspected jihadists.