Did Barcelona and Cambrils attackers botch even deadlier rampage?

Twin vehicle attacks in Spain may have killed hundreds more had the terrorists been able to execute their original plan, it has been claimed.

Police believe a cell of up to 12 people were planning to use butane gas in the Barcelona onslaught on Thursday afternoon.

They linked the attacks to an explosion at a house in Alcanar less than 24 hours earlier in which one person was killed and seven others were injured.

Authorities believe the blast was caused by a person inside "preparing an explosive device".

Head of Catalonia police Josep Lluis Trapero said that forced terrorists to scrap their original plan.

"They were preparing one or several attacks in Barcelona and an explosion in Alcanar stopped this as they no longer had the material they needed to commit attacks of an even bigger scope," he said.

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The former head of the National Counter-Terrorism Security Office, Chris Phillips, also suggested the explosion could have saved hundreds more from being killed in the truck rampages.

He told Sky News: "As soon as something like that happens, all the plans that they'd laid beforehand would have changed.

"I would imagine that the vehicle that was used was intended to be a vehicle bomb.

"If a terrorist attack happens and people are knocked over, it's terrible and of course the number of people which have died is terrible.

"But if that vehicle had been packed with explosives, it would have been multiplied.

"And if a van like that hits, for example, a shopping centre, you can expect hundreds of people to be injured and hundreds of people, potentially, to be killed.

"The fact that that bomb went off and destroyed the house on Wednesday may well have saved a lot of people's lives."

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Suicide vests worn by five suspects in the Cambrils attack could also have magnified the death toll, but were discovered to be fake .

Catalonia's interior minister, Joaquim Forn, said the bomb belts were very well made, and that authorities only determined they were phoney after a controlled explosion.

Spanish media also reported the suspects were armed with large knives.

At least 13 people were killed and dozens injured in the attack on Las Ramblas, a busy tourist pedestrian street in Barcelona. A massive manhunt is under way to find the truck driver, who fled the scene.

One woman and the five suspected terrorists behind the Cambrils vehicle attack are also dead.