Alerted by a detailed tip from Spanish colleagues, Dutch police arrested a man Thursday and questioned him on suspicion of preparing an attack on a concert in Rotterdam by an American rock band.
But the Dutch justice minister suggested later in the day that the suspect may only have sent a threatening message.
The 22-year-old man was being interrogated to determine exactly what his role was in the threat, police spokeswoman Svetlana Westermeijer said. No charges had been filed yet.
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The arrest in a town identified by Dutch media as Zevenbergen, south of Rotterdam, came hours after police canceled a performance Wednesday night by the Los Angeles band Allah-Las at a converted grain silo in the heart of the port city.
"The suspicion is that the suspect is involved in the preparation of a terrorist attack," Rotterdam Police Chief Frank Paauw said.
"There is no terror threat now anymore," he added. "There is no threat because we have arrested a suspect and the information about the threat was so specific on the location of the event that, with that arrest, we can conclude that the threat is gone."
If authorities want to prolong the suspect's detention, they will have to arraign him at a closed-door hearing with an investigative judge before the end of Friday, prosecution spokeswoman Jeichien de Graaff said.
Police searched the man's home after his arrest but released no details of anything they found. His identity wasn't released, in line with Dutch privacy guidelines.
Security and Justice Minister Stef Blok, in an interview with BNR radio, suggested the suspect may only have spread the threat on a social media platform.
"The person who spread the message has been picked up and he will be questioned," Blok said in a reference to the man's arrest. "We are very curious to hear from him why he carried out this idiotic action."
Meanwhile, a Spanish mechanic detained Thursday night while driving, apparently drunk, a white van containing a number of gas canisters close to the concert venue didn't appear to be a terror suspect. Police said a search of his home uncovered nothing to indicate he was linked to the threat.
Dutch Counterterror Coordinator Dick Schoof commended the police action and left the country's threat level unchanged at "substantial," the fourth step of a five-level scale.
It wasn't clear what the nature of the threat to the concert was, or if the band's name played any role in the threat.
In an interview with The Guardian last year, band members said they chose the word Allah — Arabic for God — because they were seeking a "holy-sounding" name and didn't realize it might cause offense.
Police in Warsaw, Poland, beefed up security for the band's performance there Thursday night, checking a few hundred fans as they arrived at the NIEBO (Heaven) club.
Joanna Konieczna, 32, was excited that she would be hearing her favorite band live.
"The events in Rotterdam did not scare me, I feel very safe in Poland," she told The Associated Press.
Spain, already on high alert following last week's deadly attacks in and near Barcelona that killed 15 people and injured more than 120 others, played a key role in the events of Wednesday and Thursday.
A Spanish counterterrorism official said Spain's Civil Guard received "an alert indicating the possibility of an attack in a concert that was going to take place in Rotterdam." The Civil Guard shared the information with Dutch authorities, said the official, who spoke anonymously.
Mike Corder reported from The Hague. AP writers Aritz Parra in Madrid and Monika Scislowska in Warsaw, Poland, contributed to this report.