The two groups lined both sides of the street in front of the Islamic Community Center of Phoenix and yelled at each other, with a line of police officers standing in the middle of the street to keep them separated, CNN affiliate KNXV reported
Jon Ritzheimer, organizer of the rally, is a former Marine, and he has no middle ground when it comes to Islam.
His T-shirt pretty much says it all: "F--- Islam." Some of the counterprotesters wore shirts that said, "Love Thy Neighbor."
The Islamic Community Center of Phoenix is the mosque that Elton Simpson and Nadir Soofi
attended for a time. They're the men who drove from Arizona to a Dallas suburb to shoot up a Prophet Mohammed cartoon contest there. Both were killed by police early this month.
Many Muslims consider demeaning depictions of Mohammed to be blasphemous and banned by Islamic law.
"This is in response to the recent attack in Texas where 2 armed terrorist(s), with ties to ISIS, attempted Jihad," the event's Facebook page said
Some 600 people said they would attend.
The rally was to start about the same time evening prayers were taking place inside the center. The rally was to feature its own cartoon contest, similar to the one targeted in Texas.
"I think the whole thing, the cartoon contest especially, I think it's stupid and ridiculous," Ritzheimer said beforehand, "but it's what needs to take place in order to expose the true colors of Islam
Local Muslim leaders say they won't be intimidated.
"The Muslim community in America is here to stay and we are also well aware of the right to speak our mind and worship how we please," Dr. Yasir Shareef, a board member of the Arizona chapter of the Council on American-Islamic Relations, said at a press conference.
The White House says there's no justification for violence at the rally.
"Even expressions that are offensive, that are distasteful, and intended to sow divisions in an otherwise tight-knit, diverse community in Phoenix cannot be used as a justification to carry out an act of violence," White House spokesman Josh Earnest said.
Police Chief Joe Yahner was personally involved in arranging public safety around the event, he told CNN affiliate KPHO.
"There's a lot of things in the works. The intelligence related to the crowd is changing all the time," he said.
Gov. Doug Ducey hoped common sense will prevail in the event, he said.
"Of course, I'm a believer in free speech and the First Amendment. I'm also a believer in good judgment and common sense," he told the affiliate.
Police were to use cameras to record the event "to capture things that go on" and were to close roads, said Sgt. Trent Crump, a Phoenix police spokesman.
So far, the event seemed to be attracting a variety of people.
"It is a very scattered group of individuals with different causes that for the most part are signing on and signing up to come to this," Crump said.
The rally comes as some groups have made a deliberate effort not to be cowed by Islamic extremists, like the ones who attacked the Paris offices of the the satirical magazine Charlie Hebdo
. The publication often featured caricatures of Mohammed.
In Washington, activist and conservative blogger Pamela Geller
of New York wanted to place ads showing cartoons of Mohammed in the capital's transit system. She hoped to show the winning cartoon from her group's contest in Texas; the one where Simpson and Soofi were killed by police.
The Washington Metro board balked. It voted to stop showing issue-oriented ads throughout its system.
A worried community
Events like this one and other developments have Muslims in the area scared, said Imraan Siddiqi with the Council on American-Islamic Relations.
"Recently, the mosques here in Phoenix actually received threatening letters -- very specific threats, saying that we are going to massacre your congregations," he said.
Ritzheimer anticipates possible problems because of the rally and says people should bring their guns.
"People are also encouraged to utilize (their) second amendment right at this event just (in case) our first amendment comes under the much anticipated attack," the event's Facebook page says.
Bikers will be there too, according to the post.
Siddiqi calls it the "intersection of Islamophobia and (the) gun culture."
"When we see these two things ... then obviously it becomes more of a concern," he said. "We're advising people ... it's better to stay clear from the event, don't engage with these people."