A group of men who call themselves the "Oath Keepers" arrived in Ferguson, Missouri, late Monday night, armed with assault rifles and decked out in military fatigues.

Their arrival came during a night of tension in the St. Louis suburb, as police and protesters once again stood toe-to-toe in Ferguson and small clashes broke out.

Peaceful demonstrations on Sunday to mark the one-year anniversary of the death of 18-year-old Michael Brown, an unarmed black teenager shot and killed by a Ferguson police officer, devolved into violence Sunday night.

On Monday, protesters once again took to the streets. Late at night, the right-wing armed group arrived.

St. Louis County Police Chief Jon Belmar called their presence "both unnecessary and inflammatory," according to NBC News.

Journalists and activists at the scene posted photos of the group standing on West Florissant Avenue, the center of the recent protests in Ferguson. It is legal to open carry these types of rifles in the state of Missouri. According to state law, people who have a valid gun permit can "openly display the firearm... unless the firearm is intentionally displayed in an angry or threatening manner."

Oath Keepers are on the scene in #Ferguson pic.twitter.com/vaJkqg9JK0 — Ryan J. Reilly (@ryanjreilly) August 11, 2015

The Oath Keepers are a self-declared patriot group whose founder is a former Army paratrooper.

Many of the group are former soldiers and police officers, according to a report from Mother Jones.

Photo via @Lumumbandele Oath Keepers here with loaded guns walking directly in front of the police and through the crowd This right is the craziest shit in the world to me .. White militia's claiming to have a diverse membership but for some reason they have zero people of color on the Ferguson patrol ...we would be gunned down if we walked the streets of our community with these same weapons .. White supremacy on steroids #whichemergency #Ferguson A photo posted by Tef Poe (@tef_poe) on Aug 10, 2015 at 11:43pm PDT

Oath Keepers state on their website that "they will not obey unconstitutional orders, such as orders to disarm the American people, to conduct warrantless searches, or to detain Americans as 'enemy combatants' in violation of their ancient right to jury trial."

Many of the posts and videos on their website focus on "prepping" for a time when they think they will have to defend the Constitution, and they believe that the government plans to impose martial law on the country.

Protesters involved in the recent demonstrations in Ferguson were not pleased to see them.

Oath Keepers have shown up in Ferguson with assault rifles. Protesters led by @TefPoe telling them to get away. pic.twitter.com/n9PNwkGNBL — Jon Swaine (@jonswaine) August 11, 2015

Members of the community were quick to point out that while the men were exercising their right to bear arms in an open carry state, the local police seemed to view them in a different light than many of the unarmed demonstrators.

Ferguson Democratic Committeewoman Patricia Bynes weighed in on what she feels is a double standard for members of the local, predominantly black, community and the group of armed white men.

People are fascinated because of Black men and women showed up carrying these rifles, what would happen? #Ferguson pic.twitter.com/1iWBeSZQtF — Patricia Bynes (@PatriciaBynes) August 11, 2015

Others echoed her sentiment. (Please note: the reference to a 12-year-old girl being arrested by police has been contradicted by the St. Louis County Police Department, who say the person arrested is an 18-year-old.)

America, where we arrest 12yo girls, but white oath keepers can rock weapons. https://t.co/ru8fOnBEuD — Raven Brooks (@ravenb) August 11, 2015

There were reports of multiple arrests on Monday evening. The St. Louis County Police Department said at least nine people were taken into custody, and reported that some protesters were throwing objects at police.