Police in the Dutch port city of Rotterdam detained the driver of a van with Spanish license plates and a number of gas tanks inside after a concert by an American rock band was canceled Wednesday night following a threat, the city’s mayor said.

Rotterdam Mayor Ahmed Aboutaleb said at a hastily arranged press conference that the van’s Spanish driver was being questioned by police. Military explosives experts were deployed to Rotterdam to examine the van, police said.

Police earlier said the concert by Los Angeles band Allah-Las was called off after Dutch police received a terror warning. Aboutaleb said the warning came from Spanish police.

He declined to give further details on the nature of the warning or where in Spain it came from, adding that it was too soon to link the van to unspecified threat directed at the concert.

“It is not yet good to say that the things are linked,” Aboutaleb said. “It still has to be established that there was a link between the van and the threat. We can’t say that yet.”

Police in Spain have been investigating the deadly vehicle attacks last week that killed 15 people in and near Barcelona. They later found bomb-making equipment that included more than 100 tanks of butane gas, nails, and 500 liters of acetone.

Rotterdam police said they took the information about a threat “seriously enough that after discussion with organizers it was decided to cancel the event.”

Concert organizer Rotown said earlier on Twitter that the concert venue, a former grain silo called Maassilo, was being evacuated because of the unspecified threat.

The show hadn’t yet started when the decision to cancel it was made.

Dutch television showed officers in body armor outside Maassilo and what appeared to be members of the band leaving the venue in a white van with a police escort.

Allah-Las is a four-piece band from Los Angeles.

In an email to The Associated Press, the band’s label, Mexican Summer, said: “Due to a potential terror threat at The Maassilo in Rotterdam, the Allah-Las show was canceled tonight.

“Details are not available at this time as the incident is still under investigation. The band is unharmed and are very grateful to the Rotterdam Police and other responsible agencies for detecting the potential threat before anyone was hurt.”

In an interview with British newspaper The Guardian last year, band members said they chose the word Allah, Arabic for God, because they were seeking a “holy sounding” name and did not realize it might cause offense.

“We get emails from Muslims, here in the U.S. and around the world, saying they’re offended, but that absolutely wasn’t our intention,” lead singer Miles Michaud told the newspaper. “We email back and explain why we chose the name, and mainly they understand.”