Celtic have launched an investigation after rival Swedish fans stormed the away section at the Friends Arena and became embroiled in a violent battle with cops.

Flares were ignited during the Europa League clash by fans in the Celtic end of the ground.

Police were also filmed battering supporters with batons as a melee erupted at half-time.

Hoops fans were caught up in the violence but their club have vigorously defended their support by insisting Swedish fans infiltrated the stands.

A spokesman for the Scottish champions said: "We are aware that a number of Swedish supporters entered the area for visiting fans and we are currently investigating events."

The violence and flare use could prove costly to Celtic, albeit it may well have been started by fans of another club.

It is understood the fans may have been supporters of AIK's fierce rivals Hammarby.