Also on Thursday, hours beforehand, a person was killed in an explosion in a house about 100 km (62 miles) southwest of Barcelona, in an incident linked to the attack, police added.It was still not clear how many attackers had been involved. In another incident, police shot dead a man who had driven a car into a police checkpoint in Barcelona, though they had no evidence that this, too, was connected with the van attack.Witnesses said the white van zigzagged at high speed down Las Ramblas, a busy avenue thronged with tourists, knocking down pedestrians and leaving bodies strewn across the ground.Islamic State's Amaq news agency said: "The perpetrators of the Barcelona attack are soldiers of the Islamic State and carried out the operation in response to calls for targeting coalition states" - a reference to a US-led coalition against the Sunni militant group.The claim could not immediately be verified.