Two people are in custody after 13 people were killed and more than 100 injured Thursday when a van ran over pedestrians in this northeastern Spanish metropolis in what police described as a terror attack.

Joaquim Forn, the head of Catalonia's regional interior ministry, told reporters that 15 of the injured were in serious condition and that the death toll was likely to rise.

Neither of the two people detained in connection with the attack was the driver of the van, the Mossos d'Esquadra - the regional police force - said on Twitter.

A third person was found dead in his car 3 kilometers (1.9 miles) from a police checkpoint where he exchanged shots with officers.

While that individual may be linked to the terrorist attack, police said that an incident in which two Mossos officers were run down by a vehicle at another checkpoint did not appear to be connected to the deadly events in Las Ramblas, an area popular with tourists.

The district was thronged with people at 3 pm when the van rammed into several vehicles before barreling down the tree-lined central pedestrian-only boulevard of the Rambla.

Mossos d'Esquadra said that the van attack was related to an explosion Wednesday night in Alcanar, a coastal town south of Barcelona, where a man was killed when gas-bombs he was handling detonated inside an abandoned house.

The aim of Thursday's assault was "to kill the maximum number of people," Mossos said on Twitter.

Amaq, a jihadi-affiliated news agency, said the attackers were "soldiers of Islamic State."

Police sources told EFE that one of the suspects in custody was Driss el-Ouakabir, believed to have rented the van used in the attack.

Ouakabir, a legal permanent resident of Spain, spent a month in pre-trial detention in 2012 after being accused of sexual assault in the Catalan town of Figueres, sources close to the terror investigation told EFE.