The suspects include five foreigners from Germany and Finland and several private security guards.

The police denied the Hells Angels had been arrested for political reasons such as connections with the far right.

There was recently a violent attack on a restaurant near Lisbon that involved two far-right gangs of bikers – Hells Angels and Red&Gold – that caused six injuries, three of which were serious.

It is also being speculated that the action comes after reports that biker gangs were preparing to settle scores at next week's annual bike meet in Faro.