13 dead in Barcelona van carnage, 'terrorists' killed in another incident

Police have announced the arrest of two suspects, identified as a Spaniard and a Moroccan, but said the driver was still on the run.

Hours later in Cambrils, a city 120 kilometres south of Barcelona, police said e they shot dead "four suspected terrorists" and left another injured in a "possible terrorist attack."

The incident in Cambrils took place in the early hours of Friday, but police gave no further details, nor did they mention whether the shooting was linked to the Barcelona attack.

Witnesses in Barcelona told of scenes of chaos and horror, with bodies strewn along the famous Las Ramblas boulevard as other people fled for their lives, screaming in panic.

The rampage in a city hugely popular with tourists from around the world is the latest in a wave of attacks in Europe where vehicles have been used as weapons of terror.

WARNING: Video below may not be suitable for sensitive viewers. 

As world leaders united in condemning the carnage, the IS propaganda agency Amaq claimed that it was carried out by "soldiers" from the jihadist group.

"We're united in grief," Spanish Prime Minister Mariano Rajoy said in a televised address after rushing to Barcelona, the biggest city in Catalonia,  a region in Spain's northeast whose separatist governement is defying Madrid.

"Above all we're united in the firm intention to defeat those who want to take our values and way of life from us."

Regional interior minister Joaquim Forn said 13 people had died and another 100 were injured in what police were treating as a "terrorist attack", warning that the death toll could rise further.

There were at least 18 nationalities among the victims who came from countries as varied as France, Venezuela, Australia, Ireland, Peru, Algeria and China, according to Spain's civil protection agency.

Belgium said one of its citizens had died in the Las Ramblas assault, while The Hague said three Dutch were injured and a Greek diplomat reported three nationals had been wounded - a woman and her two children.

Cities and monuments around the world have paid tribute to victims. 

Here's how the world has reacted to the attack.