A policeman has died after street brawls 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 died in hospital after the confrontations. He had suffered cardiac arrest.
Police said a Russian man was injured but the extent of his injuries was not immediately disclosed.
Fans from both clubs were reportedly involved in the clashes which erupted ahead of the round-of-32 match in the second-tiered European club competition.
Police were escorting some Spartak fans into the stadium but a stray group allegedly started lighting fireworks and throwing flares and objects toward 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.
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.
After the violence in Bilbao, the Europa League match went ahead and ended 2-1 to Spartak Moscow, but Athletic Bilbao went through 4-3 on aggregate.