A bus with Spanish plates and containing gas bottles was found near a music venue in Rotterdam where a concert was cancelled after a threat.
The Dutch port city's mayor, Ahmed Aboutaleb, said it was not clear if the threat and the bus were connected.
The driver, a Spaniard, was taken into police custody.
"The ring that the police set up around the concert hall led to the detention of a bus with gas bottles," said the mayor, who warned against "swift conclusions".
Police said the concert, which was to feature Californian band Allah-Las, was cancelled at around 7pm after a tip-off from Spanish police.
"Police took this information seriously enough that after discussion with the organisers it was decided to cancel the event," a Rotterdam police spokesman said.
He declined to give further details of the nature of the warning or where exactly it came from.
Police in Spain have been investigating last week's deadly vehicle attacks in Barcelona and Cambrils that killed 15 people.
As concert-goers were sent away from the Maassilo, a former grain silo complex on the Maas river, the venue was cordoned off.
Dutch TV showed officers in body armour outside and what appeared to be members of the band leaving in a white van with a police escort.
In an interview last year, band members said they chose the word All, Arabic for God, because they were seeking a "holy sounding" name and did not realise it might cause offence.
"We get emails from Muslims in the US and around the world saying they're offended, but that wasn't our intention," said lead singer Miles Michaud .
"We email back and explain why we chose the name, and mainly they understand."