Masked men are attacking Uber drivers with brass knuckles and hammers in Amsterdam

Masked men are attacking Uber drivers in the Dutch capital of Amsterdam. Groups armed with brass knuckles and hammers are targeting drivers of the car-booking service, De Telegraaf reports.

The Telegraaf said today (translated to English) that "certainly two private riders" have been attacked and reported an incident to police. The authorities noted a "very serious" incident and are investigating.

A photo posted on Dutch website at5.nl shows a scene titled "Masked thugs hounding Uberpop drivers." (In Holland, the ride-booking app is called "Uberpop.") At5.nl explains that the events unfolded on Tuesday last week and says that an Uberpop driver was surrounded by assailants and forced to stop. The mob punctured tyres, poured "fluid" on the engine of the driver's car, and then restrained its victim, holding brass knuckles against his throat.

A second Uberpop driver was also attacked by an angry mob, this one wearing clown masks and balaclavas, according to At5.nl. Instead of brass knuckles, however, a hammer was used. Several Uberpop drivers reportedly chased suspected taxi drivers in retaliation (it's not clear whether these taxi drivers were behind the attacks).

Niek van Leeuwen, a director of a taxi service called Uber Netherlands, told the Telegraaf: "This is a small group of extremely violent drivers. It is important that politics speak out against violence and for innovation."