Garland, United States: The Daesh group on Tuesday claimed responsibility for its first attack on US soil, a shooting at an event in Texas that claimed to promote ‘free speech’ that left the gunmen dead.

“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 Mohammad [PBUH],” 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 [Daesh] do terrible things,” the group announced.

It marked the first time the extremist group, which has captured swathes of territory in Syria and Iraq, claimed to have carried out an attack in the United States.

US police said two men drove up to the conference centre on Sunday in Garland, where the right-wing American Freedom Defense Initiative was organising the controversial contest showcasing cartoons mocking the Prophet, and began shooting at a security guard, who was wounded in the ankle.

Garland police officers then shot and killed both men.

According to US media reports, the two men were Elton Simpson, 31, and Nadir Soofi, 34, who shared an apartment in Phoenix, Arizona.

Simpson was being investigated by the FBI over alleged plans to travel to Somalia to wage holy war, court records show.

According to court records, Simpson was sentenced to three years’ probation in 2011 after FBI agents presented a court with taped conversations between him and an informant discussing travelling to Somalia to join “their brothers” waging holy war.

The prosecution was unable to prove that Simpson had committed a terror-related offence, but did establish he had lied to investigators when he denied having discussed going to Somalia.

The White House said that President Barack Obama had been briefed on the investigation, which Texas police said was ongoing.

“There is no form of expression that justifies an act of violence,” White House spokesman Josh Earnest said.

The American Freedom Defense Initiative, a group listed by civil rights watchdog the Southern Poverty Law Centre as an anti-Muslim hate group, had organised the event, which drew about 200 people.

At the event, attended by Dutch far-right politician Geert Wilders and AFDI co-founder Pamela Geller, supporters held an exhibition of entries to a competition to draw caricatures of the Prophet.

Commentators were quick to draw parallels to the January mass shooting at the French satirical weekly Charlie Hebdo in Paris that killed 12 people and wounded 11 more.

But the magazine’s film critic, Jean-Baptiste Thoret, the magazine’s film critic who only avoided the attack because he had been late for work said “there is absolutely no comparison”.

“You have a, as you said, a sort of anti-Islamic movement [in Texas] … the problem of Charlie Hebdo is absolutely not the same,” Thoret told Charlie Rose on PBS, according to an advance transcript released on Monday.

Gerard Biard, chief editor of the magazine, added: “We don’t organise contests. We just do our work. We comment on the news. When [Prophet] Mohammad (PBUH) jumps out of the news, we draw Mohammad.

“But if he didn’t, we didn’t. We don’t … We fight racism. And we have nothing to do with these people.”

On Twitter, Abu Hussain Al Britani, who extremist monitoring group SITE identified as British Daesh fighter Junaid Hussain, described the gunmen as “two of our brothers”

But Simpson’s father Dunston told ABC News that his son, who he said worked in a dentist’s office, simply “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.”