The world football governing body FIFA expressed "complete trust" Friday in Russia's ability to ensure a safe World Cup despite fan violence in Spain during which a policeman died.
The Basque officer suffered a heart attack Thursday as hundreds of security forces clashed with supporters of Russian club Spartak Moscow in Bilbao before the start of a Europa League match.
The local security department said the death was not "directly" linked to an injury he received in street battles with scores of Russians wearing black hoodies.
He "suddenly felt ill during the serious incidents...Despite being taken quickly to hospital, he suffered cardiac arrest," the Basque security department said.
Police said they had detained nine people -- including three Russians and a Pole -- whom Moscow's Sport Express daily identified as right-wing Spartak hooligans and left-wing Basques.
FIFA said it "deeply regrets" the incident but did not assign any blame.
"As far as security for the 2018 FIFA World Cup is concerned, FIFA has complete trust in the security arrangements and comprehensive security concept developed by the Russian authorities and the Local Organising Committee," a FIFA spokesperson told AFP.
"As demonstrated during the FIFA Confederations Cup last year, Russia's already high security standards have been adapted to meet the specific needs of such major sporting events."
Russia will be hosting its first World Cup from June 14 to July 15 after securing its rights in a ugly battle with England in 2010 that included unproven bribery allegations.
But preparations have been shadowed by fears of a repeat of the June 2016 rampage by Russian hooligans that erupted in the French port city of Marseille during the Euro tournament.
The clashes left 35 people injured and shocked the world.
Russian President Vladimir Putin only wondered dismissively at the time "how 200 of our fans could beat up several thousand English".
German police Thursday announced the arrest of one Russian hooligan wanted for the "attempted homicide" of an England supporter in the violence.
- Right-wing ultras -
Scenes of helmeted Spanish police armed with metal shields fighting Russians hurling stones and flammable objects flashed across Russian TV screens and prompted government media to rally to the supporters' defence.
"Local ultras provoked Russians," Vesti state television said in a news bulletin. "Our fans were heading to the stadium when they were attacked with firecracker bombs, which resulted in a fight."
A column on the website of Russia's main sport channel Match TV accused the police of "having insufficient experience" in dealing with converging groups of fans.
But Moscow's authoritative Sport Express daily said it was clair that "the Spartak fans are no saints".
"They really did include people with right-wing views -- including ultra-right-wings ones," Sport Express said. "And they were ready to square off against the ultra-left-wing Basques."
Hooliganism experts say Russia's powerful FSB security service has cracked down hard on football gangs and blacklisted many of their leaders in the run-up.
The Russian government's official plan is to force both foreign and domestic supporters to undergo background checks before receiving a special Fan ID card required to enter the country.
A security source said Russian law enforcement agents were also working with their counterparts from England and other countries to determine which fans were safe.