The Spanish Police investigating the terror attack in Barcelona found more than 100 tanks of highly flammable butane gas at a house in Alcanar in the Catalonia region, where a terror cell of at least 12 people was believed to have been operating, AP reported.

The house was being used as a bomb factory, according to the police. Investigators believe that the suspects in the Barcelona and Cambrils attacks wanted to use the explosive then, but could not because of an explosion at the house. Members of the terror cell had plans to use the explosives in the vans to launch a massive attack in the Catalan capital, the police said.

On August 17, a van mowed pedestrians down in Barcelona’s Las Ramblas tourist area, killing 13. The Islamic State group had claimed responsibility for the strike. The Catalan Police are still hunting for the suspected van driver, Moroccon-born Younes Abouyaaqoub. The 22-year-old lived in the town of Ripoll, north of Barcelona.

An officer of the Catalan Police Josep Lluis Trapero said investigators did not know where he was, but suspect that Abouyaaqoub may have slipped across the border into France. “We don’t have any specific information on this, but it cannot be ruled out,” he added.