The Spanish region of Catalonia has been rattled by two terror attacks and an explosion over three days, in what authorities are treating as a trio of linked incidents.

On Friday, police said the perpetrators of the attacks in Barcelona and Cambrils originally planned to use explosive devices, but their plans were foiled after bomb-making materials accidentally blew up a house – believed to be the suspects’ base – in Alcanar.

Four people have been arrested – one in Alcanar and three in Ripoll. Three were Moroccan citizens and another was Spanish; they ranged in age from 21 to 34. None were on the radar for terrorism.

It is unclear how many people were involved in the attacks and how many suspects are still on the run.

Here’s what we know so far:

Friday: Cambrils

- Source: CNN " data-fave-thumbnails="{"big": { "uri": "https://media.cnn.com/api/v1/images/stellar/prod/170818030611-03-cambrils-0818.jpg?q=x_2,y_229,h_1228,w_2182,c_crop/h_540,w_960" }, "small": { "uri": "https://media.cnn.com/api/v1/images/stellar/prod/170818030611-03-cambrils-0818.jpg?q=x_2,y_229,h_1228,w_2182,c_crop/h_540,w_960" } }" data-vr-video="false" data-show-html="" data-byline-html="
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Updated 1:03 PM EDT, Fri August 18, 2017
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An overturned car is transported on a platform from the spot where terrorists were intercepted by police in Cambrils, Spain, Friday, Aug. 18, 2017. The police force for Spain's Catalonia region says the five suspects shot and killed in the resort town of Cambrils were carrying bomb belts, which have been detonated by the force's bomb squad. (AP Photo/Emilio Morenatti)
Gunfire breaks out during Cambrils attack
01:24 - Source: CNN

- In the early hours of Friday morning, five armed attackers drove a car through a crowd of people in the town of Cambrils, 75 miles southwest of Barcelona.

- One woman was killed and six others injured, including one police officer.

- Police engaged in a shootout with the attackers, and all five were shot dead, four of them by one officer.

- The attackers were wearing fake suicide belts, had carried an ax and knives in the car, and had wounded a person in the face with a knife before being shot.

Thursday: Barcelona

- A white van plowed into pedestrians at around 5 p.m. on Las Ramblas, the city’s busiest tourist promenade.

- At least 13 people were killed and more than 120 injured in the country’s deadliest attack since the 2004 Madrid bombings.

- The driver of the van fled on foot and was believed to be still at large.

- People from at least 34 countries are among the injured, according to officials. A Belgian, two Italians and an American are among the dead.

- A second van, believed to be linked to the Barcelona van, was found in Vic, a town 43 miles from Barcelona, Reuters reported.

- A driver ran over two police officers at a security checkpoint, causing them minor injuries. It was unclear whether this was terrorism-related.

- ISIS claimed the Barcelona attack through its media wing, but offered no evidence supporting the claim.

- Source: CNN " data-fave-thumbnails="{"big": { "uri": "https://media.cnn.com/api/v1/images/stellar/prod/170817210115-las-ramblas-police.jpg?q=x_1242,y_99,h_1738,w_3088,c_crop/h_540,w_960" }, "small": { "uri": "https://media.cnn.com/api/v1/images/stellar/prod/170817210115-las-ramblas-police.jpg?q=x_1242,y_99,h_1738,w_3088,c_crop/h_540,w_960" } }" data-vr-video="false" data-show-html="" data-byline-html="
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Updated 1:03 PM EDT, Fri August 18, 2017
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Spanish policemen stand guard in a cordoned off area after a van ploughed into the crowd, killing 13 persons and injuring over 50 on the Rambla in Barcelona on August 17, 2017. A driver deliberately rammed a van into a crowd on Barcelona's most popular street on August 17, 2017 killing at least 13 people before fleeing to a nearby bar, police said. Officers in Spain's second-largest city said the ramming on Las Ramblas was a "terrorist attack" and a police source said one suspect had left the scene and was "holed up in a bar". The police source said they were hunting for a total of two suspects. / AFP PHOTO / LLUIS GENE (Photo credit should read LLUIS GENE/AFP/Getty Images)
Barcelona terror attack: How it happened
01:17 - Source: CNN

Wednesday: Alcanar

The debris of the house where an explosion killed one person in Alcanar.
The debris of the house where an explosion killed one person in Alcanar.
Jaume Sellart/EPA

- Just after 11 p.m., the fire brigade was alerted to an explosion in a house in Alcanar, a city about 100 miles southwest of Barcelona.

- One person was killed and seven others were injured. One of the injured was taken into custody on Friday.

- Police now believe the cause of the blast came from the premature detonation of explosive devices, which the suspects had intended to use in an attacks.

- Police said the person killed was a Spanish national and was not on police radar.

- Officials said the house collapsed completely and caused serious damage to the facade of the house next door.