A van veered onto a promenade and barreled down the busy walkway in central Barcelona on Thursday, swerving back and forth as it mowed down pedestrians and turned a picturesque tourist destination into a bloody killing zone. Fourteen people were killed and 100 were injured, 15 of them seriously, in what authorities called a terrorist attack.Two people were arrested but the van driver, who fled on foot, remained at large. Friday morning, a third and fourth suspect were taken into custody. Early Friday morning, police killed five suspects engaged in an attack that injured six people in a seaside resort town and that the government for Spain’s Catalonia region said was connected to the Barcelona killings.The late afternoon attack in the city’s Las Ramblas district left victims sprawled in the historic street, spattered with blood or writhing in pain from broken limbs. Others were ushered inside shops by officers with their guns drawn or fled in panic, screaming and 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 Catalonia 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.Spanish authorities released photos and information on four of the suspects on Friday.Graphic videos and photos from the scene showed multiple people sprawled and bloodied on the ground at the scene of the crash as emergency personnel attended to them.Bruno Gulotta, an Italian father-of-two, was the first named victim of the attack. He was on holiday with his partner Martina and two children, five-year-old son Alessandro and daughter Aria, who is a few months old, according to his employer."Yesterday afternoon in Barcelona the terrorists killed friend and colleague Bruno Gulotta," his employer, Tom's Hardware Italia, said in a statement Friday. "Today is a day of mourning."President Donald Trump tweeted a response to the attack, saying "The United States condemns the terror attack in Barcelona, Spain, and will do whatever is necessary to help. Be tough & strong, we love you!"Trump followed that with a tweet referencing a story about Army Gen. John Pershing using extreme measures to deal with Muslim rebels: "Study what General Pershing of the United States did to terrorists when caught. There was no more Radical Islamic Terror for 35 years!" The story has been doubted.U.S. Secretary of State Rex Tillerson said at a press conference on Thursday that the U.S. is "ready to help" and "terrorists around the world should know that the United States and its allies are determined to find them and bring them to justice."Early Friday, Catalan police said they shot and killed five suspects in response to a terrorist attack in the seaside resort town of Cambrils, south of Barcelona. They said the suspects carried bomb belts, which were detonated by a police bomb squad.Media reports said a car crashed into a police vehicle and nearby civilians and police shot the attackers, one brandishing a knife. Police did not immediately say how the attack was carried out. A police officer and five civilians were injured and two were in serious condition.Police are working on the theory that the Cambrils and Barcelona attacks are connected, as well as a Wednesday night explosion in the town of Alcanar in which one person was killed.Catalan Interior Minister Joaquin Forn told local radio RAC1 early Friday that the Cambrils attack “follows the same trail” as the Barcelona attack. “There is a connection.”He did not explain what connected the attacks but confirmed that the driver in the Barcelona attack remains at large.The Catalan regional government said citizens from 24 countries were among the people killed and injured during the Barcelona van attack.Sombre crowds gathered Friday morning for a moment's silence led by King Felipe, the Spanish head of state, at Barcelona's Plaça de Catalunya -- near where the attack began. After the silence, those present joined together in lengthy applause. "We are not afraid, we won't forget," they chanted.CNN contributed to this story.