It came ahead of a Europa League match in the Spanish city
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 clashes. He had suffered a cardiac arrest.
Police said a Russian man was wounded but the extent of his injuries were not 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.
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.
"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.