Spain terror attacks - what we know

Witnesses in Barcelona said a van zigzagged down one of city's busiest tourist avenues, Las Ramblas, mowing down pedestrians and leaving bodies strewn across the ground. Police confirmed it was a terrorist attack.

Several hours later, a speeding car killed one person and injured five in the seaside resort of Cambrils. The car's five occupants were shot dead by police. Catalonian authorities have confirmed that the two attacks were linked.

Police say they have arrested four men suspected of having a role in the attacks. They are still searching for the driver of the vehicle used in Barcelona. He is believed to be on the run, although officials have said he also could have been one of the five shot dead in Cambrils.

The so-called "Islamic State" (IS) terror group claimed responsibility for the attacks. "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," the group's news agency said.

Police said three of the detained suspects are Moroccan, and one is a Spaniard. None of them were known to have links to terror groups.

The Catalan government said that at least 13 people had died in the Barcelona attack, with 61 still receiving treatment for injuries in hospital - 17 of them in a critical condition. Four people wounded in the Cambrils attack remain in hospital. The victims came from at least 34 countries, officials said.

On Friday, thousands of people gathered around a makeshift memorial in Las Ramblas, the site where the van came to a halt. Many left flowers and candles in honor of the victims.

Spanish Prime Minister Mariano Rajoy announced three days of official mourning for what he called a "jihadist attack." At a news conference in Barcelona, he told reporters: "Today the fight against terrorism is the principal priority for free and open societies like ours. It is a global threat and the response has to be global."

King Felipe of Spain, Prime Minister Rajoy and Catalonia Regional President Carles Puigdemont join crowds gathered for a minute of silence in Las Ramblas.

Spanish authorities are also investigating the scene of an explosion late Wednesday that killed one person in the city of Alcanar, some 200 kilometers (124 miles) southwest of Barcelona. Police first thought the explosion was an accident but said Thursday they now believe an explosive device intended for use in Barcelona was being prepared in the building.