BARCELONA, Spain - A van veered onto a promenade Thursday and barreled down the busy walkway in central Barcelona, swerving back and forth as it mowed pedestrians down and turned a picturesque tourist destination into a bloody killing zone. Thirteen people were killed and 100 were injured, 15 of them seriously, in what authorities called a terror attack. 

Victims were left sprawled in the street, spattered with blood or writhing in pain from broken limbs. Others fled in panic through Las Ramblas, screaming or carrying young children in their arms.

"It was clearly a terror attack, intended to kill as many people as possible,'' Josep Lluis Trapero, a senior police official for Spain's Catalonia region told reporters late Thursday.

The Islamic State group claimed responsibility, saying in a statement on its Aamaq news agency that the attack was carried out by "soldiers of the Islamic State'' in response to the extremist group's calls for followers to target countries participating in the coalition trying to drive it from Syria and Iraq.

Authorities said a Belgian was among the dead and a Greek woman was among the injured. Germany's Foreign Ministry said it was checking reports that German citizens were among the victims.

Spanish Prime Minister Mariano Rajoy called the killings a "savage terrorist attack'' and said Spaniards "are not just united in mourning, but especially in the firm determination to beat those who want to rob us of our values and our way of life.''

After the afternoon attack, Las Ramblas went into lockdown. Swarms of officers brandishing hand guns and automatic weapons launched a manhunt in the downtown district, ordering stores and cafes and public transport to shut down. 

Several hours later authorities reported two arrests, one a Spanish national from Melilla, a Spanish-run Mediterranean seafront enclave in North Africa, and the other a Moroccan. They declined to identify them.

Trapero said neither of them was the van's driver, who remained at large after abandoning the van and fleeing on foot. The arrests took place in the northern Catalan town of Ripoll and in Alcanar, the site of a gas explosion at a house on Wednesday night. Police said they were investigating a possible link between the explosion and Thursday's attack.

Spanish public broadcaster RTVE and other news outlets named one of the detained as Driss Oukabir, a French citizen of Moroccan origin.  RTVE reported said Oukabir went to police in Ripoll to report that his identity documents had been stolen. Various Spanish media said the IDs with his name were found in the attack van and that he claimed his brother might have stolen them.

Media outlets ran photographs of Oukabir they said police had issued to identify one of the suspects. The regional police told the Associated Press that they had not distributed the photograph. They refused to say if he was one of the two detained.

Barcelona is the latest European city to experience a terror attack carried out using a vehicle as a weapon to target a popular tourist destination, after similar attacks in France, Germany, Sweden and Britain.

"London, Brussels, Paris and some other European cities have had the same experience. It's been Barcelona's turn today,'' Carles Puigdemont, president of Catalonia's government.

Thursday's bloodshed was Spain's deadliest attack since 2004, when al-Qaida-inspired bombers killed 192 people in coordinated assaults on Madrid's commuter trains. In the years since, Spanish authorities have arrested nearly 200 jihadists. The only deadly attacks were bombings claimed by the Basque separatist group ETA that killed five people over the past decade but declared a cease-fire in 2011.

"Unfortunately, Spaniards know the absurd and irrational pain that terrorism causes. We have received blows like this in recent years, but we also that terrorists can be beaten,'' Rajoy said.

Hours after Thursday's attack, the police force for Spain's northeastern Catalonia region said troopers searching for the perpetrators shot and killed a man who was in a vehicle that hit two officers at a traffic blockade on the outskirts of Barcelona. But Trapero the driver's actions were not linked to the van attack.

Las Ramblas is a wide avenue of stalls and shops that cuts through the center of Barcelona and is one of the city's top tourist destinations. It features a pedestrian-only walkway in the center while cars can travel on either side.

A taxi driver who witnessed Thursday's attack, Oscar Cano, said the white van suddenly jumped the curb and sped down the central pedestrian area at a high speed for about 500 yards (457 meters), veering from side to side as it targeted people.

"I heard a lot of people screaming and then I saw the van going down the boulevard,'' another witness, Miguel Angel Rizo, told The Associated Press. "You could see all the bodies lying through Las Ramblas. It was brutal. A very tough image to see.''

Jordi Laparra, a 55-year-old physical education teacher and Barcelona resident, said it initially looked like a terrible traffic accident.

"At first I thought it was an accident, as the van crashed into 10 people or so and seemed to get stuck. But then he maneuvered left and accelerated full speed down the Ramblas and I realized it was a terrorist attack,'' Laparra said. "He zigzagged from side to side into the kiosks, pinning as many people as he could, so they had no escape.''

Carol Augustin, a manager at La Palau Moja, an 18th-century former palace on Las Ramblas that now houses offices and a tourism center, said the van passed in front of the building.

"People started screaming and running into the office. It was such a chaotic situation. There were families with children,'' she said.

Tamara Jurgen, a visitor from the Netherlands, said she and a friend were inside a clothing store steps from the scene and were kept inside until it was safe to leave.

"We were downstairs when it happened and everyone was screaming and running. We had to run up to the roof and throw our bags over a wall,'' Jurgen said. "We were all together along this wall and we were scared we were going to have to jump.''

Barcelona Mayor Ada Colau announced a minute of silence to be held Friday in Barcelona's main square "to show that we are not scared.'' The prime minister announced three days of national mourning.

Leaders around the world offered their support and condolences to Barcelona after the attack.

US President Donald Trump wrote on Twitter: "The United States condemns the terror attack in Barcelona, Spain, and will do whatever is necessary to help. Be tough & strong, we love you!''

British Prime Minister Theresa May said the UK "stands with Spain against terror'' while French President Emmanuel Macron tweeted Thursday evening: "All my thoughts and solidarity from France for the victims of the tragic attack in Barcelona. We will remain united and determined.''

Spain has been on a security alert one step below the maximum since June 2015 following attacks elsewhere in Europe and Africa.

Cars, trucks and vans have been the weapon of choice in multiple extremist attacks in Europe in the last year.

The most deadly was the driver of a tractor-trailer who targeted Bastille Day revelers in the southern French city of Nice in July 2016, killing 86 people. In December 2016, 12 people died after a driver used a hijacked truck to drive into a Christmas market in Berlin.

There have been multiple attacks this year in London, where a man in a rented SUV plowed into pedestrians on Westminster Bridge, killing four people before he ran onto the grounds of Parliament and stabbed an unarmed police officer to death in March.

Four other men drove onto the sidewalk of London Bridge, unleashing a rampage with knives that killed eight people in June. Another man also drove into pedestrians leaving a London mosque later in June. (AP)