The fundamentalist terrorist organization the Islamic State claimed responsibility Tuesday via its official radio station for the attempted terrorist attack against an anti-Muslim event in Texas showcasing cartoons depicting the Prophet Mohammad.It was the first attack by the fundamentalist Islamic organization on US soil since the inception of the organization."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 Muhammad," the group said."We tell America that what is coming will be even bigger and more bitter, and that you will see the soldiers of ISIS do terrible things," the group added.Texas police shot dead two gunmen who opened fire on last Sunday outside an exhibit of caricatures of the Prophet Mohammad that was organized by a group described as anti-Islamic and billed as a free-speech event.Citing a senior FBI official, ABC News identified one of the gunmen as Elton Simpson. The Arizona man was the target of a terror investigation. FBI agents and a bomb squad were searching Simpson's Phoenix home, ABC said.Phoenix's KPHO TV reported that the second man lived in the same apartment complex as Simpson, the Autumn Ridge Apartments. He was not identified, and the second man's apartment was searched, the station said, quoting an FBI agent. FBI spokeswoman Katherine Chaumont in Dallas said she had no more information about the suspects. An FBI evidence team began to go over the scene at 4:15 a.m. CST (0915 GMT) and was still working, she said in an email.The shooting in a Dallas suburb was an echo of past attacks or threats in other Western countries against art depicting the Prophet Mohammad. In January, gunmen killed 12 people in the Paris offices of French satirical magazine Charlie Hebdo in what it said was revenge for its cartoons.The attack on Sunday took place at about 7 p.m. local time in a parking lot of the Curtis Culwell Center, an indoor arena in Garland, northeast of Dallas. Geert Wilders, a polarizing Dutch politician and anti-Islamic campaigner who is on an al Qaeda hit list, was among the speakers at the event.Garland police and the FBI had no immediate comment on the report.A fighter for Islamic State, a militant group which has taken over large parts of Iraq and Syria, said in a tweet that "2 of our brothers just opened fire at the Prophet Muhammad (s.a.w.) art exhibition in Texas," according to the SITE Intelligence Group, a US-based monitoring group.SITE identified the writer as "Abu Hussain AlBritani," a name used by British Islamic state fighter Junaid Hussain.Shortly before midnight, police alerted media that a strong electronic pulse would be activated near the scene, presumably as part of the bomb squad's work, and a loud boom was heard moments later, though police did not comment further.The exhibit was organized by Pamela Geller, president of the American Freedom Defense Initiative (AFDI). Her organization, described by the Southern Poverty Law Center as a hate group, has sponsored anti-Islamic advertising campaigns in transit systems across the country. Organizers of the "Muhammad Art Exhibit and Contest" said the event was to promote freedom of expression. They offered a $10,000 prize for the best artwork or cartoon depicting the Prophet, as well as a $2,500 "People's Choice Award."Depictions of the Prophet Mohammad are viewed as offensive in Islam, and Western art that portrays the Prophet has angered Muslims and provoked threats and attacks from radicals.Reuters contributed to this report.