About 75 protesters gathered on Friday in Arizona outside a mosque for an anti-Islam demonstration featuring cartoons of the Prophet Mohammad, weeks after a similar event in Texas came under attack from two gunmen who had worshiped at the Phoenix center.Some protesters were armed and carrying guns at the event outside the Islamic Community Center of Phoenix. The event was organized by an Iraq war veteran who posted photos of himself online wearing a T-shirt with the slogan "Fuck Islam" on it and waving the US flag."This is in response to the recent attack in Texas," organizer Jon Ritzheimer wrote on his Facebook page, suggesting demonstrators should come with weapons in case our First Amendment "comes under much anticipated attack."More than 900 people responded on the event's Facebook page that they would take part in the Phoenix demonstration that started about 6 p.m. local time (0100 GMT on Saturday), even as others strongly criticized the planned demonstration.Caricatures of the Prophet Mohammad, which many Muslims view as blasphemous, have been a flashpoint for violence in Europe and the United States in recent months where those displaying or creating such images have been targeted by militants.Meanwhile, anti-Muslim groups have been active in the United States, buying ads and staging demonstrations characterizing Islam as violent, often citing the murderous brutality of Islamic State militants in Iraq and Syria.The Phoenix mosque targeted on Friday has condemned such violence, and held a series of sermons at Friday prayers last year by an imam who criticized militant Islamist groups like Islamic State, al-Qaida and Nigeria's Boko Haram.The president of the center urged worshippers not to engage with the demonstrators."We should remind ourselves that we do not match wrongness with wrongness, but with grace and mercy and goodness," Usama Shami told worshippers during Friday afternoon prayers.Phoenix police planned to have a presence throughout the neighborhood where the mosque is situated, said spokesman Sergeant Trent Crump.In January, gunmen killed 12 people at the Paris office of the satirical magazine Charlie Hebdo in anger at the magazine's cartoons featuring the Prophet, and a similar attack was foiled in Texas on May 3.The pair of gunmen who opened fire near Dallas outside an exhibit of cartoons featuring Mohammad were shot dead by police without killing anyone. Leaders of the Phoenix Muslim community confirmed both gunmen had attended the Phoenix mosque targeted in Friday's demonstration.Todd Green, a religion professor at Luther College in Iowa who studies Islamophobia, said that the brutal acts committed by Islamic State and other militant groups have colored many Americans' impressions of Muslims."Almost two-thirds of Americans don't know a Muslim," Green said. "What they know is ISIS, al Qaeda, and Charlie Hebdo."US officials are investigating claims that the Texas gunmen had ties to the Islamic State, but said they had not established a firm connection.The Department of Homeland Security has been in touch with state and local law enforcement authorities, and was monitoring the situation in Phoenix, White House spokesman Josh Earnest said."Even expressions that are offensive, that are distasteful, and intended to sow divisions in an otherwise tight-knit, diverse community like Phoenix, cannot be used as a justification to carry out an act of violence, and certainly can't be used as a justification to carry out an act of terrorism," he told reporters.Ritzheimer, the main organizer of the demonstration, said the point of the contest to draw caricatures of Mohammad was "to expose the true colors of Islam.""True Islam is terrorism. Yes, the ones that are out committing these atrocities and stuff, they are following the book as it's written," Ritzheimer told CNN.Ritzheimer was a staff sergeant in the Marine Reserve and was deployed to Iraq twice, in 2005 and 2008, the Marine Corps said.