Austin, Texas - Three people were killed and 14 wounded in a shooting overnight in downtown Austin, the capital of Texas, which the FBI said Sunday may have been an "act of terrorism."

The gunman, who was not identified, was among the dead, Austin police chief Lisa Davis said at a press conference.

FBI special agent Alex Doran said an exact motive was not known, but "there were indicators on the subject and in his vehicle that indicate a potential nexus to terrorism."

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"In terms of specifically what type of terrorism, we're just at this point prepared to say that it was potentially an act of terrorism," Doran said.

The FBI's Joint Terrorism Task Force was brought in to participate in the investigation alongside local authorities.

The shooting comes amid heightened security in many American cities following the launching of US and Israeli air strikes on Iran, which killed the country's supreme leader Ali Khamenei and several other senior officials.

Davis said the assailant was shot by police who responded swiftly to the shooting, which took place around 2:00 AM CT in Austin's entertainment district.

The officers "were faced with the individual with a gun and three of our officers returned fire, killing the suspect," the police chief said.

Davis said the gunman first opened fire with a pistol from his car on patrons of Buford's Backyard Beer Garden in downtown Austin.

He then parked his car and emerged with a rifle and began shooting at people who were walking by, Davis said.

Three of the wounded were in critical condition, officials said.