THE HAGUE, Netherlands — 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 cancelled 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.