Four civilians carrying military-style rifles and sidearms patrolled a riot-torn street in Ferguson, Missouri, early Tuesday, saying they were there to protect a media organization but drawing swift criticism from police and protesters alike.

The appearance of the four men, all white, quickly drew stares in the mostly black neighborhood, which exploded into violence again on Sunday night as protesters marked the police killing of an unarmed black teen a year ago.

The men identified themselves as part of a group called "Oath Keepers," which describes itself as an association of current and former U.S. soldiers and police who aim to protect the U.S. Constitution.

The Southern Poverty Law Center, a non-profit civil rights organization, has described the "Oath Keepers" as a "fiercely anti-government, militaristic group," and St. Louis County Police Chief Jon Belmar condemned their appearance in Ferguson.

"Their presence was both unnecessary and inflammatory," he said, adding that police would work with county prosecutors to see if the men had broken any laws.

Led by a man who gave his name only as John, the group, whose members wore bulletproof vests and carried sidearms in addition to combat-style rifles, said they had come to protect a journalist from the conservative "Infowars.com" Web site.

"There were problems here, there were people who got hurt. We needed to be prepared for that," said the man, who noted that Missouri state laws generally allow the open carrying of heavy weapons of the kind that his group were brandishing.

InfoWars could not be reached for immediate comment.

Ferguson has seen months of violent protest since the fatal shooting of 18-year-old Michael Brown by a white police officer a year ago. Sunday night's protests were punctuated by gunfire, with police shooting and critically wounding a man who they said had opened fire on them.

Monday's protests were less chaotic, with about nine people arrested in skirmishes with police that saw protesters throw rocks and bottles at officers.

But many in the crowd questioned the wisdom of openly carrying such heavy weapons into an emotionally charged situation.

"You’re going to bring some uncommissioned citizens, white citizens, into a black community like this? It's disrespectful," said Talal Ahmad, 30, who is black and has been a fixture of the last year's protests, which prompted a Justice Department review that found Ferguson's police department routinely violated city residents' civil rights.

"Here, in a black neighborhood, we’re already living in a state of terror," Ahmad said.