Investigators believe the Islamic extremist cell which carried out the vehicle rampages in Barcelona and the resort of Cambrils may have accidentally blown up the Alcanar property while preparing explosives a day earlier.
One of those killed in Wednesday’s blast at the alleged bomb factory may have been former imam, Abdelbaki es Satty, who is said to have been a spiritual ringleader of the group.
Police said they have discovered 120 gas canisters at the property for attacks.
They believe the cell wanted to fill three rental vans with explosives to create a massive atrocity.
But the plans changed after the house where their plot was being hatched blew up.
The possible bomb maker Mohamed Houli Chemlal was wounded in the explosion and is being detained.
Authorities also said the driver of the van that knocked down pedestrians on Barcelona’s Las Ramblas promenade on Thursday, killing 13 people and injuring over 120, was the only terrorist in the vehicle.
But there is confusion over who was at the wheel at the time of the rampage.
The driver could have been Younes Abouyaaquoub who is still being hunted and may have since crossed the French border.
Authorities have linked three vans to Abouyaaquoub, a 22-year-old of Moroccan origin, whose credit card was used to rent them.
It was earlier claimed that Moussa Oukabir was driving. He was killed along with four other terrorists by officers following a stand-off in Cambrils.
A civilian died and several others were hurt in the car rampage, along with an officer.
However, police have now told reporters they cannot say for sure who drove the van into crowds at Las Ramblas.
Another van was found in Vic, 44 miles north of Barcelona on the road to Ripoll, where all the main attack suspects lived.
A third was found in Ripoll itself.