MADRID, Feb. 22 (Xinhua) -- A member of the Erzaintza (Basque Regional Police Force) is confirmed to have died during incidents provoked by supporters of Russian side Spartak Moscow before Thursday's Europa League game against Athletic Club Bilbao on Thursday night.

The city of Bilbao had been on high alert with 600 police and 200 private security staff on duty in the expectation of the arrival of 2,500 Spartak supporters, several hundred of whom were known to belong to Spartak's notorious ultras, who provoked incidents in the nearby city of Vitoria on Monday night.

Bilbao had been calm until around 19.45 hours when the most violent of the Spartak 'fans' provoked a series of incidents close to the San Mames Stadium throwing bottles, golf balls and fireworks and setting off flares.

That provoked a series of charges by the Erzaintza and confrontation between the police and the Russian supporters, during which the police officer suffered a heart attack.

He was rapidly transferred to the nearby Basurto Hospital, but was confirmed by the Basque Regional Government to have died at around 22.00 hours.

"There have been five arrests, we don't know if they are Spartak supporters, but a number of them are Russian," a spokesman for the Ertzaintza told the local media.

The incident takes place less than four months before Russia is due to host the 2018 World Cup finals, and will do little to calm security worries among fans considering visiting the tournament.