Tear gas has emerged as the weapon of choice for French riot police confronting Yellow Vests protesters, and its use has drawn condemnation from French protesters and human rights organisations alike.

The Montpellier office of the League for Human Rights (LHR) has reportedly addressed concerns over the "massive and prolonged use" of tear gas at Yellow Vests demonstrations to the head of the Herault department, which Montpellier falls under.

The organisation is said to have identified some fifteen cases in which respiratory problems commonly associated with "acute toxicity" were observed.

"People have been getting gassed for 20 weeks and we have no feedback from clinical studies on this," Sophie Mazas, president of the LDH in Montpellier, was quoted as saying.

"We demand that law enforcement be carried out in accordance with the precautionary principle, the health of people and the right to demonstrate," she added, urging authorities to "analyse this phenomenon and take it in hand".

It came after several witnesses were "struck" by the power of the gases emitted to disperse the crowds during protests on 30 March, according to the French daily Midi Libre.

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The tear gas issue came under increased scrutiny in February, when some protesters complained about what they called cyanide poisoning as a result of police actions.

For example, Paris lawyer Raquel Garrido claimed that she had suffered from "stomach pains and spasms" as well as vomiting and headache.

"I informed my friends [on Facebook] about my symptoms following the inhalation of [tear] gas yesterday at Act 13," she tweeted on 10 February.

"Since then, I have received a lot of similar testimonials. According to my doctor, this resembles hydrocyanic acid poisoning. I demand that the Interior Ministry reveals the composition of the gas."

When pressed on the issue, Secretary of State to the Minister of Interior Laurent Nunez rebuffed accusations that the tear gas used against the protesters contained poisonous substances.

"There are no products kept secret [in the tear gas composition]," Nunez said, adding that it contains "no incapacitating product" and that its recipe has remained unchanged.

Yellow Vest rallies first emerged in France in mid-November over a proposed increase in fuel taxes. While the government backed down on its plans and introduced some measures to improve the socioeconomic situation, protesters continue to take to the streets across the country every weekend to express their discontent with government policies.

According to the French Interior Ministry, almost 4,000 people have been injured in protests since the launch of the movement.