A Catholic priest on Chicago’s South Side claims he has received death threats from gun-rights advocates following a weekend rally in front of a local gun shop that authorities say is the number one supplier of guns recovered from crime scenes in the city.

Father Michael Pfleger, the pastor of Saint Sabina church, says the threats originate from social media posts and internal emails from the Illinois State Rifle Association (ISRA), an affiliate of the wider National Rifle Association (NRA), and its supporters which are calling Pfleger a “terrorist” and likening him and similar advocates to Isis, the terrorist organisation also known as Islamic State.

The threats escalated last weekend when Pfleger led about 300 people in front of Chuck’s Gun Shop & Pistol Range in suburban Riverdale, an effort in coordination with the Brady Centre to Prevent Gun Violence in Washington. NRA members staged a counter-protest. According to Pfleger, local police barred his assembly from entering the shop door to meet with its owner and forced them to walk back and forth between two assembled NRA groups where they were verbally threatened. He also says he received many threatening emails and phone calls at his church before and after the event.

“We would like to tell Pfleger one thing: Come for our guns and you will know what hell on earth is all about – Got it?” read one email, he said.

“This is craziness,” Pfleger says. “If anything, it reminded me how much more aggressive we want to be” in raising awareness of illegal gun purchases.

Rich Pearson, the ISRA executive director, says he stands by his effort to label Pfleger a “terrorist”.

“You have to call him what he is. He’s an anti-gun terrorist, he’s trying to destroy businesses, he’s trying to prevent people from having the right of self-defence,” Pearson says.

According to local media reports, an internal email sent to ISRA members painted Pfleger as delivering “frothy-lipped lunacy” and suggested that “few will forget Pfleger’s rant in front of Chucks several years ago when he called for the Isis-style murders of gun shop owners and elected officials who support gun rights.”

Pearson says the Isis reference is connected to comments Pfleger made several years ago when he suggested he wanted to “snuff out” state legislators and gun shop owners who refuse to concede to stronger gun control measures. Pfleger admits he used the phrase, but says he intended to say he wanted to “sniff out” where gun rights advocates live to suggest it is not the inner city where their actions have the severest consequences.

“They keep trying to go back to that [statement], but it is their manipulation of the word without putting it into the context of the sentence,” he said. “If you want to own a gun, fine, but for God’s sake, put some responsibility on the ownership.”

Pearson says Pfleger is dodging responsibility: “That’s hogwash. He said the word ‘snuff’ and everybody knew what it meant. So he actually said what he meant, he just doesn’t like it now.”

The debate has tightened focus on the Riverdale gun shop, where 8% of all guns recovered from Chicago crime scenes between 2009-2013 were purchased, Chicago police say. To them, gun shops like Chuck’s need stricter regulation, such as video camera installations, inventory audits, licence transfers, and employee background checks.

However, Pearson says the shop should not be penalised for “straw” purchases, or street sales, which pass the gun from a legal owner who has passed federal background checks, among other regulations, to someone who could not. But Chicago police say that, because 35% of the guns traced back to Chuck’s were recovered within three years of the original purchase date, it suggests the sales involved either criminal behaviour by the buyer or the dealer. They add it is often difficult to prove that dealers “looked the other way” when they suspect a straw purchaser is at their counter.

Arthur Lurigio, a criminologist at Loyola University in Chicago, says because the homicide clearance rate is so low – Chicago police cleared 126 of the 415 murders last year – the police often struggle to recover guns used in shootings in order to trace them back to their rightful owner.

“[Pfleger] should be marching outside police headquarters,” he says. “If they recover guns used in shootings, they should be able to track where the gun was purchased and then track the person who purchased the gun, and then you can discover if the owner of the gun shop is really adhering to the law.”

Nevertheless, experts who study hate groups warn that heightened rhetoric can have tragic consequences. They point to the Kansas doctor George Tiller who was gunned down at his church in 2009 by an anti-abortion activist following years of being labelled a “baby killer” across social media.

Mark Potok, an expert on extremism at the Southern Poverty Law Centre in Montgomery, Alabama, says the NRA has “a moral responsibility” to moderate its language.

“Talking about terrorists and Isis demonises a person to a point where they actually may be targeted for death,” says Potok. “I don’t accuse the NRA of trying to murder the priest but the NRA is sicking people on this person. When you make these kind of statements, you can’t be surprised when the priest get death threats because words have consequences.”

Pfleger says he is deeply worried that “guns have become a first line of offence in how we handle our problems in America.” The threats, however, have not deterred his advocacy.

“I’d be ridiculous to say that there’s not concern because I’ve had everyone in the world tell me their concerns,” he says. “But does that hinder me in any way? No, not at all.”