A South African company has built a drone designed to shower pepper spray on unruly crowds and says it has begun supplying units to an international mining company.

Desert Wolf claims it wants to help in "preventing another Marikana" – a reference to a protest in August 2012 at which 34 striking mineworkers were shot and killed during clashes with the police.

But the "Skunk Riot Control Copter" was condemned by labour activists as "absolutely outrageous" and compared with deadly US military drones in Pakistan.

Desert Wolf is marketing the 500,000 rand (£27,400) machine, unveiled at a recent trade show, as "designed to control unruly crowds without endangering the lives of the protesters or the security staff".

It says the Skunk boastscan eight electric motors with 16-inch propellors, lifting 45kg and carrying 4,000 pepper-spray paintballs, plastic balls or other "non-lethal" ammunition. The device is equipped with four barrels firing up to 20 balls per second each, which could equate to 80 pepper balls per second "stopping any crowd in its tracks".

The firm's website states: "The operator has full control over each marker. He can select the RED paint marker and mark the protester who carries dangerous weapons, he can select the BLUE marker to mark the vandalising protestors and if needed the pepper balls to stop the advancing crowd before they get into a 'life threatening situation'."

The Skunk is also fitted with bright strobe lights, "blinding lasers" and on-board speakers to enable communication and warnings to the crowd. It has a thermal camera and high-definition video camera with on-board recording.

Desert Wolf insists: "Our aim is to assist in preventing another Marikana; we were there and it should never happen again."

South African police check the bodies of striking workers shot dead near Marikana platinum mine in August 2012. Photograph: EPA

On a single afternoon in Marikana, police gunned down 34 striking mineworkers in the bloodiest act by security forces since the end of racial apartheid in 1994. The killings are the subject of an ongoing commission of inquiry. Ten others, including police and security guards died in clashes that week.

Hennie Kieser, managing director of Desert Wolf, said he was flying drones at Marikana at the time as part of the surveillance operation.

"Anyone who was at Marikana would rather have this technology than live ammunition," he continued. "People who say it's inhumane compared to 9mm bullets are idiotic."

Kieser insisted: "It's the best solution for both parties: the miners on strike and those who are trying to control the strike. They both want to go home to their wives at the end of the day."

He said an international mining house had ordered 25 of the unmanned aerial vehicles but he is not permitted to disclose its identity, or say where it operates. There is also interest from mining and security companies in South Africa and beyond, he said. Current aviation rules in South African prevent the drones being deployed but he hopes the legislation can be changed.

There was an immediate backlash against the technology. James Nichol, a British lawyer representing the families of dead strikers at Marikana, said: "It's absolutely outrageous. Using pepper spray like ammunition to scatter the crowd. People are entitled to be on strike. Who would make the decision? It's absurd."

He added: "What we know about drones is in Pakistan they have killed funeral parties and they have killed wedding parties. Innocent people would be caught up in this. It seems to be the thin end of the wedge.

"One of the lessons of Marikana is that the state should stay out of industrial disputes. If they want people firing back at drones which then crash and hurt innocent people, be it on their heads. It's disgraceful."

Rehad Desai, spokesperson for the Marikana Support Campaign and director of a documentary film, Miners Shot Down, said: "The government are increasingly turning to authoritarian methods instead of dialogue and mediation. It's to be expected that they would adopt such equipment to quell dissent. But the more violent the equipment, the more violent the reaction will be.

"Why would it be more 'humane' to pepper spray people on their way home than to shoot them? I don't see the analogy."

Tim Noonan, a spokesman for the International Trade Union Confederation, told the BBC: "This is a deeply disturbing and repugnant development and we are convinced that any reasonable government will move quickly to stop the deployment of advanced battlefield technology on workers or indeed the public involved in legitimate protests and demonstrations."

South Africa's platinum belt is currently deadlocked in a strike which, after five months, is the longest in the history of the country's mines and has pushed many workers and their families into dire poverty and hunger.