Russia practising tight security ahead of 2018 World Cup
Russia is using Champions League matches involving English clubs to prepare it for hosting next summer's World Cup.
Organisers say the 2018 tournament will be one of the "most protected" ever - as the country faces threats from terror and hooligans.
Some 2,000 British fans are in Moscow as Liverpool play Spartak Moscow and Manchester United face CSKA Moscow on Tuesday and Wednesday respectively.
Authorities are using the fixtures as dummy runs for security ahead of the World Cup.
Hooliganism in Russian football has been a matter of growing concern over recent years.
So-called Russia "ultras" were involved in clashes with England fans during the 2016 Euro Championships in Marseilles.
Many Russians were believed to have come trained, equipped and determined to cause carnage in the French port.
But Russia's president Vladimir Putin has introduced a string of tough measures targeting sports hooligans in the past six months.
These included tough new sentencing for people who cause trouble - both Russian and foreign.
Russia's role in the conflict in Syria means the threat from terror is continuing to grow.
But organisers predict the 2018 World Cup will be one of the "safest" and "most protected" yet.
This will entail levels of security never seen before.
Fans travelling to Russia for the tournament can expect to go through several layers of security before even entering a stadium.
Once inside, police will monitor activity inside the grounds from a central control room, using hundreds of individual cameras attached to seats.
Organisers also say that spectators will know exactly where the line is when it comes to behaviour.