A French animal rights group has faced a huge backlash after a video showed some of its members forcibly taking a puppy away from a homeless man in central Paris. Footage of the incident, which occurred earlier in September, shows three Cause Animale Nord activists dragging the dog away from the man, who wails as he attempts to stop them.

Nghi Le Duc, who posted the video on Facebook, said he was shocked when he saw the scene on the streets of the city, writing that the activists "violently, mercilessly" took a "homeless man's friend".

The film has been viewed more than 1.7 million times and shared by tens of thousands of people. A photo is now circulating from the Cause Animale Nord Facebook page, showing that the the puppy - which has been named Vegan - has been put up for adoption for a fee of €195 (£144).

The caption accompanying the picture reads: "Vegan (named in honour of our beliefs), a little dog, rescued at the Marche. We took it from a Roma who was begging. The police do nothing, we act. You too can take action, it just takes a little courage. [The dog] will be put up for adoption."

After receiving a fierce backlash ranging from angry comments to death threats, the rights group defended the move, claiming the puppy had been drugged so it would stay calm and help the man beg for more money, and that it was not chipped or vaccinated. In a statement, Cause Animale Nord's chairman, Antony Blanchard, said the dog had dilated pupils and its cries heard on the video "are not normal".

"We know how important the presence of an animal is for people living on the street" but the group "cannot condone the exploitation and abuse of animals for commercial ends", he said. "If the state services did their work we would not have to."

More than 120,000 people have so far signed a petition calling for an investigation into the incident. "Nowhere does it stipulate that [the group] has the right to remove an animal without warning. That's what they did by violently attacking a homeless person to remove his puppy around the Chatelet area of Paris," the petition reads. "To justify this act of extreme violence, they allege that the homeless person is a Roma and that the animal was drugged, it hadn't been vaccinated or had ID and was malnourished."