At least 13 people are dead and more than 80 injured after a van was driven into pedestrians on Barcelona's Las Ramblas, says The Scotsman.
Catalan police arrested two people after the white Fiat van tore through the street, which was packed with shoppers and holidaymakers at the time, says The National.
The Telegraph reports how 70 miles away, in the town of Cambrils, at least six people were hurt when "alleged terrorists" drove into pedestrians before being shot dead by security forces.
Police believe the incidents may be linked, says The Times, which also reports that Spanish police were trying to piece together a family mystery amid reports that a man named as a suspect in the Barcelona attacks may have had his documents stolen by his younger brother.
Catalonian officials said of those arrested over the Barcelona attack, one was from Morocco and one from Melilla, a Spanish enclave in North Africa. Neither man is believed to be the driver, who remains at large, writes the i newspaper.
Likewise, the Daily Express writes that a terrorist who rammed a van into shoppers on Las Ramblas, could still be on the run in Barcelona as police reveal he is not among those arrested.
Also, The Scottish Sun says that the "sick driver" responsible for the twisted ISIS-claimed van attack in Barcelona that killed at least 13 people and injured 100 is still being hunted by brave Spanish cops.
The Daily Mail says ISIS has claimed responsibility for the massacre of 13 innocent pedestrians after a terror attack in the heart of Barcelona left more than 100 injured, ten of them critically.
The extremists have promised "horror and panic" from "individual wolves" who are "still waiting for the right time to cover your heads and shed your blood", writes the Daily Record, which quotes from an apparent admission of responsibility from those behind the attack.
In other news, The Herald continues its coverage of the row over election expenses in the Liberal Democrats. A second Lib Dem MP is facing questions after an investigation by the paper, which says Christine Jardine - who gained Edinburgh West in one of the toughest contests in the country - disregarded thousands of pounds of costs on her official candidate declaration.
Dundee road crashes cost society £7.5m last year, according to The Courier, which also reports that 29 people were injured as a result, while one of the crashes resulted in a fatality.