Patrick Howley claimed he infiltrated Saturday's DC protest in order to discredit it – but account has since been altered

A conservative US news magazine has come under fire after one of its journalists boasted of being an agent provocateur at a clash between protesters and security guards in Washington.

The incident, in which guards used pepper spray on protesters trying to enter the Smithsonian's National Air and Space Museum, was widely reported to be linked to the Occupy Wall Street protests.

Patrick Howley, an assistant editor at the American Spectator, wrote over the weekend that he had infiltrated the protest group in order to discredit it. He said: "As far as anyone knew I was part of this cause — a cause that I had infiltrated the day before in order to mock and undermine in the pages of the American Spectator — and I wasn't giving up before I had my story."

However, Howley's breathless account of his role as provocateur – which goes on to condemn the protesters' "lack of nerve to confront authority", and his own determination to escalate the protest further as he rushed past security guards into the museum – has since been altered. The magazine appears to have taken down the story, although it has been reported in the Washington Post and on the Firedoglake and Daily Kos blogs.

Removed from the new story is any mention of Howley's motive to "mock and undermine" the protesters, or his disdain for their "lack of nerve". Instead, he says his involvement was intended for journalistic purposes, and that he rushed inside the museum "to find a place to observe."

Charlie Grapski, a citizen journalist and activist, accused the American Spectator and Howley of breaching journalistic integrity, and of criminal acts – and called for them to be investigated and charged.

Grapski said: "It is not journalism. This goes against every tenet of ethical journalism. Howley was doing it in order to 'mock and undermine'. His actions shows that the protesters were not out to disrupt, but that chaos and disruption followed his actions. Not only has he distorted the story to discredit others, he has engaged in criminal acts."

"They should be charged with criminal acts and inciting a riot."

Grapski added: "The changes to the story are designed to eliminate the admission of guilt and to eliminate his role as provocateur."

Kenneth Lipp, an activist at Occupy Wall Street, also called for Howley to be charged with inciting a riot.

"If any of the protesters had done that, they would be charged," Lipp said.

He said that there were "obvious provocateurs" in the movement, and that a committee had been set up to identify them, and to warn others about them.

"There are provocateurs down at the park. We can't really call them out but they are obvious people who are not supporters of the protest. We have the safe occupation committee in Washington or the security committee in New York to help root out the provocateurs and to keep people safe."

Saturday's march, organised by a group called the October 11 movement to protest against the US government's use of unmanned drones overseas, was attended by members of the Occupy Wall Street movement's Washington branch. Howley's account reports that he and a small number of protesters had tried to move past the security guards blocking entrance to the museum, and they were pepper-sprayed. Tourists and one female security guard were also pepper-sprayed in the ensuing melee, according to reports.

According to his initial account, Howley then tried to provoke further clashes, rushing upstairs past the guards.

"I forced myself into the doors and sprinted blindly across the floor of the Air and Space Museum, drawing the attention of hundreds of stunned khaki-clad tourists … I wasn't giving up before I had my story," he wrote.

"I strained to glance behind me at the dozens of protesters I was sure were backing me up, and then I got hit again, this time with a cold realisation: I was the only one who had made it through the doors …"

He concludes his piece by praising the guards who pepper-sprayed him, saying they "acted with more courage that I saw from any of the protesters."