A policeman has died after street fights broke out between officers and rival football fans outside a Spanish stadium.
Police in riot gear faced off against hundreds of fans outside the San Mames Stadium in Bilbao before a Europa League match on Thursday night between hosts Athletic Bilbao and Spartak Moscow.
Authorities said a police officer, named by Spanish media as 51-year-old Inocencio Alonso Garcia, died in hospital after the confrontations. He had suffered a cardiac arrest.
Police said a Russian man was wounded but the extent of his injuries was not immediately disclosed.
Fans from both clubs were reportedly involved in the clashes which erupted before kick-off.
Police were escorting some Spartak fans into the stadium, but a stray group allegedly started lighting fireworks and throwing flares and objects towards Athletic supporters and officers.
The fighting spread on to the streets near the stadium. Stones were thrown at police, who set off flares to push back crowds.
Many fans were seen trying to run away from the trouble as fireworks exploded all around.
Spanish Prime Minister Mariano Rajoy offered his condolences to the family of the policeman who died and condemned the violence.
In a statement, UEFA said it "strongly condemns the violent clashes which occurred in Bilbao. We are in contact with local authorities to obtain further information on these incidents".
More than 500 police officers were deployed ahead of the game to try and prevent fan trouble.
Police made a number of arrests as the violence and injuries escalated.
"Five people have been arrested. We do not know if they are all supporters of Spartak, but many of them are Russians," a regional police spokesman said.
After the violence in Bilbao, the tie went ahead and ended 2-1 to Spartak Moscow, but Athletic Bilbao went through 4-3 on aggregate.
Meanwhile, a Russian football hooligan wanted for savagely attacking an England fan during Euro 2016 in France was arrested in Germany - on his way to the Europa League match.
"Police detained the wanted man on his arrival in Erdinger Moos from Moscow," a German police statement said, adding the 31-year-old risks up to 15 years in jail in France for attempted homicide and grievous bodily harm.French authorities had for months been seeking the suspect, who was not named and, along with several other Russian hooligans, is accused of attacking 51-year-old England fan Andrew Bache ahead of the Russia-England match in Marseille.
Mr Bache was left paralysed on the left-hand side of his body after being hit around the head with an iron bar.
French authorities issued an arrest warrant for the Russian suspect in December 2017 after months of work with British police to identify the perpetrators of the assault.
Russia is hosting the World Cup from 14 June and authorities are putting strict security procedures in place to try to prevent violence.
Six years ago, a fan died in Bilbao in clashes after a match between Athletic and German club Schalke.