The Islamic State (IS, formerly ISIS) made a statement on Tuesday, claiming this was the terrorist group’s first attack on US soil. The IS added that two of its “soldiers” had attempted to carry out an attack as the exhibit was “portraying negative pictures of the Prophet Mohammed,” AFP reported.

The jihadist group warned that this could be start of a terror campaign that will be “bigger and more bitter.”

Both gunman were shot and killed in a parking lot outside the venue, which was hosting a controversial art event depicting images of the Prophet Mohammed.

The shooters were named as roommates Elton Simpson and Nadir Soofi, from Phoenix. It emerged that Simpson had been under surveillance since 2006. In 2011, he was convicted of committing a terror-related offense after lying to FBI agents about his desire to travel to Somalia and join jihadist militia.

media accounts, which had possible links to the Islamic State (IS), posted messages referring to Sunday’s attacks before they were carried out.

A Twitter account under the name “Shariah is Light” posted a message with the hashtag #texasattack at 18.35 Central Time. An image on the account featured American-born jihadist Anwar al-Awlaki, who was killed in 2011 in Yemen by a drone attack.

The Shariah is Light account subsequently attempted to follow a second account “AbuHussainAlBritani.” This second account posted a number of messages referring to the shooting in Texas and appeared to imply that IS was behind it.

One of the tweets said that “2 of our brothers just opened fire" at the Prophet Muhammad art exhibition in Texas.

The incident unfolded when a car drove up towards an indoor arena in Garland, where in the region of 200 people had been attending the exhibit, which offered a $10,000 first prize for the best artwork or cartoon depicting the prophet.

Artist Bosch Fawstin won the award for his drawing of a sword-wielding Prophet in a turban saying, “You can’t draw me.”

The event was organized by the American Freedom Defense Initiative (AFDI), which is led by Pamala Geller, a critic of Islam. It emerged that the AFDI paid $10,000 for extra security and protection.

Geller’s organization decided to create the ‘Mohammed Art Exhibition and Contest’ following the Charlie Hebdo massacre in Paris in January after the satirical magazine had published cartoons mocking the Prophet.

Following the shooting, Geller, who has been behind a series of anti-Hamas adverts displayed on transportation networks across the US, wrote a statement on her website saying that "This is war on free speech."

The prize was presented to Fawstin, who was a former Muslim, by the controversial Dutch politician Gert Wilders, who gave a 15 minute speech to the audience, in which he said, “We are here to defend our rights and stand for freedom of speech.” He also declared that similar exhibitions should be held “all over the United States and all over the free world.”

Last week, two Democrat lawmakers had asked President Barack Obama to prevent the far-right politician from being allowed to enter the US for his anti-Muslim views. Before speaking in Texas, he had met with Republican Senators Louie Gohmert and Steve King.