An FBI crime scene investigator documents the area around two deceased gunmen and their vehicle Monday in Garland, Texas. Police shot and killed the men after they opened fire on a security officer.

WASHINGTON — The target of a federal terror investigation was one of two suspects in a shooting at a Texas cartoon contest featuring images of the Muslim Prophet Muhammad, and the Islamic State group today claimed responsibility for the attack.

An audio statement on the extremist group’s Al Bayan radio station said “two soldiers of the caliphate” carried out Sunday’s attack in the Dallas suburb of Garland. It did not provide details and it was unclear whether the group was opportunistically claiming the attack as its own.

It was the first time that IS, which frequently calls for attacks against the West, had claimed responsibility for one in the United States.

The gunmen, whom federal officials identified as Elton Simpson and Nadir Soofi, wounded a security officer before they were shot and killed at the scene. The officials spoke on the condition of anonymity.

The deliberately provocative cartoon contest had been expected to draw outrage from the Muslim community. According to mainstream Islamic tradition, any physical depiction of the Prophet Muhammad — even a respectful one — is considered blasphemous, and drawings similar to those featured at the Texas event have sparked violence around the world.

Simpson and Soofi were wearing body armor, and one shot the security officer in the leg. Garland police spokesman Joe Harn said Monday that a single Garland police officer subdued the two gunmen but that after his initial shots, SWAT officers nearby also fired at the two men. Harn said police don’t know who fired the lethal shots.

The security officer was treated at a hospital and released.

Simpson, of Phoenix, was arrested in 2010 after a four-year-long terror investigation. The government prosecuted him on only one minor charge.