By Girish Gupta and Christian Veron

CARACAS (Reuters) - Venezuela's opposition protests on Wednesday may be the messiest in a six-week wave of unrest as demonstrators prepare to throw feces at security forces, adding to the customary rocks, petrol bombs and tear gas.

The new tactic has been dubbed the "Poopootov" in a play on the Molotov cocktails often seen at streets protests in Venezuela.

"They have gas; we have excrement," reads an image floating around social media to advertise Wednesday's "Shit March."

With inflation in the high triple-digits, shortages of the most basic medicines, and millions suffering food scarcity, the country is undergoing a major crisis.

For weeks, hundreds of thousands of people have taken to the streets, angry at the government of unpopular President Nicolas Maduro.

Some opposition sympathizers are appalled at the plans to use feces, both animal and human, calling it an unsanitary and inappropriate tactic even in the face of a government they despise.

Many note that throwing feces could increase cases of infectious diseases which are soaring due to the lack of medicine as well as basic cleaning materials such as soaps and disinfectant.

"POOPOOTOV COCKTAIL"

"The kids go out with just stones. That's their weapon. Now they have another weapon: excrement," said a 51-year-old dentist preparing containers of feces in her home for protesters to launch at authorities.

"One of my patients is collecting excrement from her child," said the dentist, who asked not to be identified.

Messages have been going viral on Venezuelan WhatsApp groups giving step-by-step instructions and advice on putting together the Poopootov cocktails.

Some insist on avoiding glass containers to ensure that the projectiles only humiliate troops rather than injure them.

"The use of excrement is not only an act of desperation, it's madness," said pro-government TV personality Mario Silva on Twitter.

With opposition leaders looking to bring frontline government forces onside, given they too suffer from the country's crisis, the strategy may backfire.

Many are thought to sympathize with protesters' complaints about the economic situation but do not speak out for fear of retaliation by authorities.

While the opposition coalition has remained quiet on the strategy, some lawmakers have given it tacit acceptance.

"They use their weapons against us, so people are using what they have," said lawmaker Rafael Guzman, who on Monday was seen in the thick of tear gas throwing a canister back at security forces.

(Reporting by Girish Gupta and Christian Veron; Additional reporting by Deisy Buitrago; Editing by Andrew Hay and Michael Perry)