Isis have claimed responsibility for the vehicle ramming attack in Las Ramblas, Barcelona.
At least 13 people were killed and 100 more were hurt when a van ploughed into pedestrians in a busy tourist district.
Isis have claimed responsibility for a number of other terrorist attacks in Europe, including vehicular attacks.
The extremist group's claim was made on their news agency Amaq.
A message said: "The perpetrators of the attack in Barcelona are Islamic State soldiers and carried out the operation on command of Khilafah of targeting coalition countries".
The "coalition" refers to the US-led force fighting Isis in Iraq and Syria.
Isis often quickly claim responsibility for terrorist attacks in Europe and elsewhere, even if they have been carried out by so-called 'lone wolves'.
But Rita Katz, director of the SITE intelligence group, said the Amq claim was "preceded by celebration from ISIS community, possibly indicating group's knowledge of plan".
The group has been suffering severe losses on the battlefield recently, losing Mosul, its major urban stronghold in Iraq, in July.
Experts fear this could prompt Isis to adapt more guerilla warfare-type tactics in Western cities.
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