It marked the first time the extremist group, which has captured swathes of territory in Syria and Iraq using brutal methods, claimed to have carried out an attack in the United States.
But it was unclear if the claim was credible or whether the two gunmen had simply gained inspiration for the attack from the IS group’s macabre propaganda, officials said.
“Two of the soldiers of the caliphate executed an attack on an art exhibit in Garland, Texas, and this exhibit was portraying negative pictures of the Prophet Mohammed,” the jihadist group said.
“We tell America that what is coming will be even bigger and more bitter, and that you will see the soldiers of the Islamic State do terrible things,” the group said.
Police said the two men drove up to the conference center Sunday in Garland, where the anti-Muslim, right-wing American Freedom Defense Initiative was organizing a controversial Mohammed cartoon contest, and opened fire with assault rifles, hitting a security guard in the ankle.
A Garland police officer then shot and killed both men using his service pistol.
The two suspected jihadists were Elton Simpson, 31, and Nadir Soofi, 34, who shared an apartment in Phoenix, Arizona.
A day after FBI agents searched the apartment where the two men lived, a portrait of Simpson began to take shape, as acquaintances recalled his passion for basketball and his youthful conversion to Islam.
But there were scant details available about Soofi, except that he had owned a struggling pizza and hot wings restaurant. Managing his business reportedly meant he sometimes had to skip prayers at the mosque.
According to a Facebook page, Soofi graduated from the International School of Islamabad, in Pakistan, in 1998, and attended the University of Utah. A cousin told local media Soofi was born in the United States.
Simpson was convicted in 2011 of lying to the FBI about his plans to travel to Somalia. Federal prosecutors accused him of wanting to wage “violent jihad” there but a judge found the government had failed to prove that charge. Simpson was sentenced to three years’ probation.
But the FBI reportedly started investigating Simpson again in recent months after he began posting about the IS group on social media.
Simpson’s online activity was monitored and he was placed under occasional surveillance, though authorities saw no sign that he planned to stage an attack, according to media reports.
Usama Shami, president of the Islamic Community Center of Phoenix, which both men had attended, said they were “regular people” who gave no indication of being radicalized.
Simpson was well-liked among the young men at the mosque, he said.
Kristina Sitton, a Phoenix attorney who represented Simpson in his court case, said she was shocked by the news.
Sitton said she could not imagine why Simpson had turned to violence.
“I can only think that he must have snapped at the event that was taking place there,” she said.
Many Muslims find drawings of the prophet to be disrespectful or outright blasphemous, and such cartoons have been cited by Islamists as motivation in previous attacks.
But White House spokesman Josh Earnest said: “There is no form of expression that justifies an act of violence.”
The American Freedom Defense Initiative, a group listed by civil rights watchdog the Southern Poverty Law Center as an anti-Muslim hate group, had organized the event, which drew about 200 people.
Attended by Dutch far-right politician Geert Wilders and AFDI co-founder Pamela Geller, the event featured an exhibition of entries to a competition to draw caricatures of the Prophet Mohammed.
AFDI had offered a $10,000 prize for the winner of the contest, billed as a “free speech” event.
The winning entry reportedly showed a scowling Mohammed wearing a turban and saying “You can’t draw me!”
Under the cartoon was the caption, “That’s why I draw you.”
The paper identified the winner as Bosch Fawstin, a New York native born to Albanian Muslim immigrants.
Commentators have drawn parallels to the January mass shooting at the French satirical weekly Charlie Hebdo in Paris that killed 12 people and wounded 11 more.
Simpson’s father Dunston told ABC News that his son, who he said worked in a dentist’s office, “made a bad choice.”
“We are Americans and we believe in America,” Dunston Simpson said. “What my son did reflects very badly on my family.” – AFP