Watch: Jon Stewart angrily confronts known conspiracy theorist over veterans bill
Actor turned activist Jon Stewart gives remarks at a PACT Act rally to support funding veterans who are victims of burn pit related illnesses. (Shutterstock.com)

Jon Stewart was caught on video getting visibly angry this Monday at a known conspiracy theorist and right-wing activist over the veteran bill he's fighting to get passed.

Jack Posobiec, who helped popularize a conspiracy theory claiming Hillary Clinton was running a child sex trafficking ring out a pizza parlor and who pushed unfounded claims about the murder of former DNC staffer Seth Rich, showed up outside Capitol Hill as Stewart was promoting his lobbying efforts.

While it's not known what exactly precipitated Stewart's anger, the two ended the encounter in a positive note, with Stewart saying he mistook Posobiec for a "troll" and Posobiec saying he actually supports the legislation, known as the PACT Act, that would help thousands of veterans suffering from cancer, respiratory illness and other ailments.

So-called burn pits have been commonly used by the US military in post-September 11 conflicts, and are lit to get rid of everything from plastic bottles to human waste to old tires -- all incinerated with the aid of jet fuel.

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But the fumes from these open fires are now suspected of causing a range of illnesses among soldiers who were deployed at such bases, from chronic respiratory ailments to a variety of cancers.

President Joe Biden himself says he thinks these pits were at the root of the brain cancer that claimed the life of his son Beau, who served in Iraq in 2008.

The Department of Veterans Affairs estimates that some 3.5 million US service members were exposed to toxic smoke in Afghanistan, Iraq or other conflict zones, and more than 200,000 veterans have registered on lists of people who came into contact with burn pits.

Watch video below or at this link.

With additional reporting by AFP