Dutch police Thursday released a van driver arrested over a suspected terror attack plot on a Rotterdam concert venue, but stepped up inquiries based on a "concrete" tip-off from Spain.
"The man was freed earlier this evening and is no longer a suspect in the investigation," Rotterdam police said in a statement.
It remained unclear whether the tip-off by Spanish officials to the Dutch was linked to last week's deadly attacks in Catalonia. Nor was it clear when the Spanish learned of the threat.
The twin vehicle attacks in northwest Spain killed 15 people and wounded 120 others.
Dutch investigators are still trying to piece together the events that led to the cancellation of Wednesday night's concert by Californian rock band.
Earlier Thursday, Rotterdam police chief Frank Paauw told AFP: "There was concrete information from the Spanish police that an attack would be committed on that date, at this place and against this rock band."
After cancelling the planned concert, police carried out a pre-dawn raid where they arrested "a 22-year-old man regarding the terror threat Wednesday evening in Rotterdam," a police statement said.
BNR radio cited sources that the man had been arrested after "making threatening statements" over the messaging app Telegram, said to be popular with terror groups.
Justice Minister Stef Blok later told BNR radio the authorities were "keen to hear why he had done something so idiotic".
This man was still in detention, said Paauw, "suspected of being involved in preparations for a terror attack".
Dutch national news agency ANP said the suspect was most likely a student from the small town of Zevenbergen, described by neighbours as "a quiet youngster with a girlfriend".
'Wrong place, time'
The driver of the Spanish-plated van was arrested Wednesday evening after police noticed him driving in a suspicious way, near the concert venue at the Maassilo, in the city's sprawling harbour district.
Even on Wednesday however, there were doubts that he was in fact linked to the threat.
While officers found a "couple of gas canisters" in the van, the driver was a mechanic who "appeared to be under the influence of an alcoholic substance," police said.
Spanish police also ruled the man out of the inquiry. They said he had "five gas canisters in his van for domestic use" but was completely drunk.
Police chief Paauw said it looked as if "the man had had the bad luck to be in the wrong place at the wrong time".
The threat on the concert venue recalls previous such attacks.
In May, 22 people were killed in a suicide bombing at a concert by US singer Ariana Grande in the northern English city of Manchester.
And in November 2015, 90 people were killed in Paris at the Bataclan concert hall where US rock band Eagles of Death Metal were playing.
That was part of a coordinated jihadist attack on the city that night which claimed 130 lives.
In Rotterdam on Wednesday, the members four-piece band from Los Angeles, were escorted from the concert hall by police wearing bullet-proof vests.
In a statement sent to AFP, the band said they were "unharmed and are very grateful to the Rotterdam police and other responsible agencies for detecting the potential threat before anyone was hurt".
They later said they were "looking for a new date to reschedule the performance".
The band performed Thursday as planned in the Polish capital Warsaw, with lead singer Miles Michaud telling around 300 cheering fans "it's not like last night" before the Los Angeles-based quartet launched into a set of their trademark psychedelic rock.
Warsaw police said there was no evidence suggesting that an incident earlier Thursday involving a 24-year-old Israeli citizen, who lightly wounded a police officer close to the concert venue, was in anyway related to the performance.
Rotterdam mayor Ahmed Aboutaleb said Thursday afternoon the "specific threat surrounding that concert was over, which is logical since the concert was cancelled", his spokesman confirmed to AFP.
The Netherlands has so far been spared the terror strikes that have rocked its European neighbours recently.
But top Dutch security and intelligence officials have been keeping a wary eye on events.
In June, a Dutch man - known to authorities as being possibly radicalised - was arrested filming outside a stadium during a concert. He was later freed, but the incident is still under investigation.